Nutrient Cycling in Pastures

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LIVESTOCK SYSTEMS GUIDE

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By Barbara BellowsNCAT Agriculture SpecialistDecember 2001

Abstract: Good pasture managementpractices foster effective use andrecycling of nutrients. Nutrient cyclesimportant in pasture systems are thewater, carbon, nitrogen, and phosphoruscycles. This publication provides basicdescriptions of these cycles, and presentsguidelines for managing pastures toenhance nutrient cycling efficiency —with the goal of optimizing forage andlivestock growth, soil health, and waterquality. Includes 19 Tables and 14Figures.

Table of ContentsIntroduction and Summary ........................................................... 2Publication Overview ................................................................... 5Chapter 1. Nutrient Cycle Components, Interactions, and ............. Transformations ........................................................................ 6

Water Cycle ........................................................................... 6Carbon Cycle ....................................................................... 10Nitrogen Cycle ..................................................................... 13Phosphorus Cycle ................................................................ 18Secondary Nutrients ............................................................ 21

Chapter 2. Nutrient Availability in Pastures ................................ 23Soil Parent Material .............................................................. 23Soil Chemistry ...................................................................... 23Prior Management Practices ................................................ 24Soil Compaction ................................................................... 24Organic Matter ..................................................................... 25Soil pH ................................................................................. 27Timing of Nutrient Additions ................................................. 27

Chapter 3. Nutrient Distribution and Movement in Pastures ...... 30Pasture Nutrient Inputs and Outputs .................................... 30Manure Nutrient Availability .................................................. 32Pasture Fertilization ............................................................. 33Grazing Intensity .................................................................. 34Diversity and Density of Pasture Plants ............................... 36

Chapter 4. The Soil Food Web and Pasture Soil Quality ........... 40Diversity of the Soil Food Web ............................................. 40Organic Matter Decomposition............................................. 40Primary Decomposers ......................................................... 41Secondary Decomposers ..................................................... 43Soil Organisms and Soil Health ........................................... 44

Chapter 5. Pasture Management and Water Quality ................ 47Risk Factors for Nutrient Losses .......................................... 47Pathogens............................................................................ 48Nitrate Contamination .......................................................... 49Phosphorus Contamination .................................................. 49Subsurface Drainage ........................................................... 51Riparian Buffers ................................................................... 52Riparian Grazing .................................................................. 53

References ................................................................................ 55Resource List ............................................................................ 61

Agencies and Organizations ................................................ 61Publications in Print ............................................................. 61

Web Resources ......................................................................... 63

mailto:[email protected]?subject=Nutrient Cycling in Pastures

//NUTRIENT CYCLING IN PASTURESPAGE 2

As a pasture manager, what factors do you look at as indicators of high production and maximumprofitability? You probably look at the population of animals stocked within the pasture. You probablylook at the vigor of plant regrowth. You probably also look at the diversity of plant species growing in thepasture and whether the plants are being grazed uniformly. But do you know how much water seepsinto your soil or how much runs off the land into gullies or streams? Do you monitor how efficiently yourplants are taking in carbon and forming new leaves, stems, and roots through photosynthesis? Do youknow how effectively nitrogen and phosphorus are being used, cycled, and conserved on your farm? Aremost of these nutrients being used for plant and animal growth? Or are they being leached into thegroundwater or transported through runoff or erosion into lakes, rivers, and streams? Do you know howto change your pasture management practices to decrease these losses and increase the availability ofnutrients to your forages and animals?

Effective use and cycling of nutrients iscritical for pasture productivity. As indicated inFigure 1 above, nutrient cycles are complex andinterrelated. This document is designed to helpyou understand the unique components of wa-ter, carbon, nitrogen, and phosphorus cycles andhow these cycles interact with one another. Thisinformation will help you to monitor your pas-tures for breakdowns in nutrient cycling pro-cesses, and identify and implement pasture man-agement practices to optimize the efficiency ofnutrient cycling.

WATER

Water is necessary for plant growth, for dis-solving and transporting plant nutrients, and forthe survival of soil organisms. Water can also be adestructive force, causing soil compaction, nutri-ent leaching, runoff, and erosion. Management

practices that facilitate water movement into thesoil and build the soil’s water holding capacitywill conserve water for plant growth and ground-water recharge, while minimizing water's poten-tial to cause nutrient losses. Water-conservingpasture management practices include:• Minimizing soil compaction by not overgraz-

ing pastures or using paddocks that have wetor saturated soils

• Maintaining a complete cover of forages andresidues over all paddocks by not overgraz-ing pastures and by implementing practicesthat encourage animal movement across eachpaddock

• Ensuring that forage plants include a diver-sity of grass and legume species with a vari-ety of root systems capable of obtaining wa-ter and nutrients throughout the soil profile

Healthy plant growth provides plant cover over the entire pasture. Cover from growing plants and plant residues protectsthe soil against erosion while returning organic matter to the soil. Organic matter provides food for soil organisms thatmineralize nutrients from these materials and produce gels and other substances that enhance water infiltration and thecapacity of soil to hold water and nutrients.

Animal Production Manure Production

Water Availability

Water Infiltration

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Minimal SoilErosion

Soil Organisms

Plant Vigor

Nutrient AvailabilitySoil Organic Matter

Plant CoverSoil Porosity/Minimal Compaction

NutrientMineralization

Legumes

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//NUTRIENT CYCLING IN PASTURES PAGE 3

CARBON

Carbon is transformed from carbon dioxideinto plant cell material through photosynthesis.It is the basic structural material for all cell life,and following the death and decomposition ofcells it provides humus and other organic com-ponents that enhance soil quality. Plant nutri-ents such as nitrogen and phosphorus are chemi-cally bound to carbon in organic materials. Forthese nutrients to become available for plant use,soil organisms need to break down the chemi-cal bonds in a process called mineralization. Ifthe amount of carbon compared to other nutri-ents is very high, more bonds will need to bebroken and nutrient release will be slow. If theamount of carbon compared to other nutrientsis low, fewer bonds will need to be broken andnutrient release will proceed relatively rapidly.Rapid nutrient release is preferred when plantsare growing and are able to use the nutrientsreleased. Slower nutrient release is preferredwhen plants are not actively growing (as in thefall or winter) or if the amount of nutrients inthe soil is already in excess of what plants canuse. Pasture management practices that favoreffective carbon use and cycling include:• Maintaining a diversity of forage plants with

a variety of leaf shapes and orientations (toenhance photosynthesis) and a variety ofroot growth habits (to enhance nutrient up-take). A diversity of forages will provide abalanced diet for grazing animals and a va-riety of food sources for soil organisms

• Promoting healthy regrowth of forages byincluding a combination of grasses with bothlow and elevated growing points, and bymoving grazing animals frequently enoughto minimize the removal of growing points

• Maintaining a complete cover of forages andresidues over all paddocks to hold soil nu-trients against runoff and leaching losses andensure a continuous turnover of organic resi-dues

NITROGEN

Nitrogen is a central component of cell pro-teins and is used for seed production. It existsin several chemical forms and various microor-ganisms are involved in its transformations. Le-gumes, in association with specialized bacteria

called rhizobia, are able to transform atmosphericnitrogen into a form available for plant use. Ni-trogen in dead organic materials becomes avail-able to plants through mineralization. Nitrogencan be lost from the pasture system through thephysical processes of leaching, runoff, and ero-sion; the chemical process of volatilization; thebiological process of denitrification; and throughburning of plant residues. Since it is needed inhigh concentration for forage production and canbe lost through a number of pathways, nitrogenis often the limiting factor in forage and crop pro-duction. Productive pasture management prac-tices enhance the fixation and conservation of ni-trogen while minimizing the potential for nitro-gen losses. Practices that favor effective nitro-gen use and cycling in pastures include:• Maintaining stable or increasing percentages

of legumes by not overgrazing pastures andby minimizing nitrogen applications, espe-cially in the spring

• Protecting microbial communities involvedin organic matter mineralization by minimiz-ing practices that promote soil compactionand soil disturbance, such as grazing of wetsoils and tillage

• Incorporating manure and nitrogen fertiliz-ers into the soil, and never applying these ma-terials to saturated, snow-covered, or frozensoils

• Avoiding pasture burning. If burning is re-quired, it should be done very infrequentlyand by using a slow fire under controlled con-ditions

• Applying fertilizers and manure accordingto a comprehensive nutrient managementplan

PHOSPHORUS

Phosphorus is used for energy transforma-tions within cells and is essential for plantgrowth. It is often the second-most-limiting min-eral nutrient to plant production, not only be-cause it is critical for plant growth, but also be-cause chemical bonds on soil particles hold themajority of phosphorus in forms not availablefor plant uptake. Phosphorus is also the majornutrient needed to stimulate the growth of algaein lakes and streams. Consequently, the inad-vertent fertilization of these waterways with run-off water from fields and streams can cause


degradation of water quality for drinking, recre-ational, or wildlife habitat uses. Regulations onthe use of phosphorus-containing materials arebecoming more widespread as society becomesincreasingly aware of the impacts agriculturalpractices can have on water quality. Pasturemanagement practices must balance the need toensure sufficient availability of phosphorus forplant growth with the need to minimize move-ment of phosphorus from fields to streams. Pas-ture management practices that protect this bal-ance include:

• Minimizing the potential for compactionwhile providing organic inputs to enhanceactivities of soil organisms and phosphorusmineralization

• Incorporating manure and phosphorus fer-tilizers into the soil and never applying thesematerials to saturated, snow-covered, or fro-zen soils

• Relying on soil tests, phosphorus indexguidelines, and other nutrient managementpractices when applying fertilizers and ma-nure to pastures

SOIL LIFE

Soil is a matrix of pore spaces filled with wa-ter and air, minerals, and organic matter. Al-though comprising only 1 to 6% of the soil, liv-ing and decomposed organisms are certainly ofthe essence. They provide plant nutrients, cre-ate soil structure, hold water, and mediate nutri-ent transformations. Soil organic matter is com-posed of three components: stable humus,readily decomposable materials, and living or-ganisms — also described as the very dead, thedead, and the living components of soil (1).

Living organisms in soil include larger faunasuch as moles and prairie dogs, macroorganismssuch as insects and earthworms, and microor-ganisms including fungi, bacteria, yeasts, algae,protozoa, and nematodes. These living organ-isms break down the readily decomposable plantand animal material into nutrients, which arethen available for plant uptake. Organic matterresidues from this decomposition process aresubsequently broken down by other organismsuntil all that remains are complex compoundsresistant to decomposition. These complex endproducts of decomposition are known as humus.

Humus, along with fungal threads, bacterialgels, and earthworm feces, forms glues that holdsoil particles together in aggregates. These con-stitute soil structure, enhance soil porosity, andallow water, air, and nutrients to flow throughthe soil. These residues of soil organisms also en-hance the soil's nutrient and water holding ca-pacity. Lichens, algae, fungi, and bacteria formbiological crusts over the soil surface. Thesecrusts are important, especially in arid range-lands, for enhancing water infiltration and pro-viding nitrogen fixation (2). Maintaining a sub-stantial population of legumes in the pasture alsoensures biological nitrogen fixation by bacteriaassociated with legume roots.

Effective nutrient cycling in the soil is highlydependent on an active and diverse communityof soil organisms. Management practices thatmaintain the pasture soil as a habitat favorablefor soil organisms include:• Maintaining a diversity of forages, which

promotes a diverse population of soil organ-isms by providing them with a varied diet

• Adding organic matter, such as forage resi-dues and manure, to the soil to provide foodfor soil organisms and facilitate the forma-tion of aggregates

• Preventing soil compaction and soil satura-tion, and avoiding the addition of amend-ments that might kill certain populations ofsoil organisms

Soil contains 1-6% organic matter. Organic mattercontains 3-9% active microorganisms. These organismsinclude plant life, bacteria and actinomycetes, fungi, yeasts,algae, protozoa, and nematodes.

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Soil Organic Matter

Soil MicrobialBiomass

Soil

Readilydecomposable

7-21%Fauna 10%

Fungi 50%

Yeast, algae,protozoa,

nematodes10%

Bacteria &Actinomycetes 30%

Mineralparticles

Stable Humus70-90%

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This publication is divided into five chapters:

1. Nutrient cycle components, interactions, and transformations2. Nutrient availability in pastures3. Nutrient distribution and movement in pastures4. The soil food web and pasture soil quality5. Pasture management and water quality

The first chapter provides an overview of nutrient cycles critical to plant production and water-quality protection: the water, carbon, nitrogen, phosphorus, and secondary-nutrient cycles. Thecomponents of each cycle are explained, with emphasis on how these components are affected bypasture management practices. The description of each cycle concludes with a summary of pasturemanagement practices to enhance efficient cycling of that nutrient.

The second chapter focuses on the effects of soil chemistry, mineralogy, and land-managementpractices on nutrient cycle transformations and nutrient availability. Management impacts discussedinclude soil compaction, organic matter additions and losses, effects on soil pH, and consequences ofthe method and timing of nutrient additions. The chapter concludes with a summary of pasturemanagement practices for enhancing nutrient availability in pastures.

The third chapter discusses nutrient balances in grazed pastures and the availability of manure,residue, and fertilizer nutrients to forage growth. Factors affecting nutrient availability include nutri-ent content and consistency of manure; manure distribution as affected by paddock location andlayout; and forage diversity. These factors, in turn, affect grazing intensity and pasture regrowth. Agraph at the end of the chapter illustrates the interactions among these factors.

The fourth chapter describes the diversity of organisms involved in decomposing plant residuesand manure in pastures, and discusses the impact of soil biological activity on nutrient cycles andforage production. The impacts of pasture management on the activity of soil organisms are ex-plained. A soil health card developed for pastures provides a tool for qualitatively assessing thesoil’s ability to support healthy populations of soil organisms.

The publication concludes with a discussion of pasture management practices and their effects onwater quality, soil erosion, water runoff, and water infiltration. Several topical water concerns arediscussed: phosphorus runoff and eutrophication, nutrient and pathogen transport through subsur-face drains, buffer management, and riparian grazing practices. A guide for assessing potential wa-ter-quality impacts from pasture-management practices concludes this final chapter.

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INFILTRATION AND

WATER HOLDING CAPACITY

Water soaks into soils that have a plant orresidue cover over the soil surface. This covercushions the fall of raindrops and allows themto slowly soak into the soil. Roots create poresthat increase the rate at which water can enterthe soil. Long-lived perennial bunch-grass formsdeep roots that facilitate water infiltration by con-ducting water into the soil (3). Other plant char-acteristics that enhance water infiltration are sig-nificant litter production and large basal cover-age (4). In northern climates where snow pro-vides a substantial portion of the annual waterbudget, maintaining taller grasses and shrubsthat can trap and hold snow will enhance waterinfiltration.

The water, carbon, nitrogen, phosphorus, and sulfur cycles are the most important nutrient cyclesoperating in pasture systems. Each cycle has its complex set of interactions and transformations aswell as interactions with the other cycles. The water cycle is essential for photosynthesis and thetransport of nutrients to plant roots and through plant stems. It also facilitates nutrient loss throughleaching, runoff, and erosion. The carbon cycle forms the basis for cell formation and soil quality. Itbegins with photosynthesis and includes respiration, mineralization, immobilization, and humusformation. Atmospheric nitrogen is fixed into plant-available nitrate by one type of bacteria, con-verted from ammonia to nitrate by another set of bacteria, and released back to the atmosphere by yetanother group. A variety of soil organisms are involved in decomposition processes that release ormineralize nitrogen, phosphorus, sulfur, and other nutrients from plant residues and manure. Bal-ances in the amount of these nutrients within organic materials, along with temperature and mois-ture conditions, determine which organisms are involved in the decomposition process and the rateat which it proceeds.

Pasture management practices influence the interactions and transformations occurring withinnutrient cycles. The efficiency of these cycles, in turn, influences the productivity of forage growthand the productivity of animals feeding on the forage. This chapter examines each of these cycles indetail and provides management guidelines for enhancing their efficiency.

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Water is critical for pasture productivity. Itdissolves soil nutrients and moves them to plantroots. Inside plants, water and the dissolved nu-trients support cell growth and photosynthesis.In the soil, water supports the growth and re-production of insects and microorganisms thatdecompose organic matter. Water also can de-grade pastures through runoff, erosion, andleaching, which cause nutrient loss and waterpollution. Pro-ductive pasturesare able to absorband use water ef-fectively for plantgrowth. Goodpasture manage-ment practices promote water absorption bymaintaining forage cover over the entire soil sur-face and by minimizing soil compaction by ani-mals or equipment.

Geology, soil type, and landscape orientationaffect water absorption by soils and water move-ment through soils. Sloping land encourageswater runoff and erosion; depressions andfootslopes are often wet since water from upslopecollects in these areas. Clay soils absorb waterand nutrients, but since clay particles are very

A forage cover overthe entire paddock pro-motes water infiltrationand minimizes soilcompaction.

small, these soils can easily become compacted.Sandy soils are porous and allow water to entereasily, but do not hold water and nutrientsagainst leaching. Organic matter in soil absorbswater and nutrients, reduces soil compaction,and increases soil porosity. A relatively smallincrease in the amount of organic matter in soilcan cause a large increase in the ability of soils touse water effectively to support plant produc-tion.


layer or high water table. Soils prone to satura-tion are usually located at the base of slopes, nearwaterways, or next to seeps.

Impact on crop production. Soil saturationaffects plant production by exacerbating soil com-paction, limiting air movement to roots, andponding water and soil-borne disease organismsaround plant roots and stems. When soil poresare filled with water, roots and beneficial soil or-ganisms lose access to air, which is necessary fortheir healthy growth. Soil compaction decreasesthe ability of air, water, nutrients, and roots tomove through soils even after soils have dried.Plants suffering from lack of air and nutrientsare susceptible to disease attack since they areunder stress, and wet conditions help disease or-ganisms move from contaminated soil particlesand plant residues to formerly healthy plant rootsand stems.

Runoff and erosion potential. Soil satura-tion enhances the potential for runoff and ero-sion by preventing entry of additional water intothe soil profile. Instead, excess water will runoff the soil surface, often carrying soil and nutri-ents with it. Water can also flow horizontallyunder the surface of the soil until it reaches thebanks of streams or lakes. This subsurface wa-ter flow carries nutrients away from roots, wherethey could be used for plant growth, and intostreams or lakes where they promote the growthof algae and eutrophication.

The Water Cycle. Rain falling on soil can either beabsorbed into the soil or be lost as it flows over the soilsurface. Absorbed rain is used for the growth of plants andsoil organisms, to transport nutrients to plant roots, or torecharge ground water. It can also leach nutrients throughthe soil profile, out of the reach of plant roots. Water flowingoff the soil surface can transport dissolved nutrients asrunoff, or nutrients and other contaminants associated withsediments as erosion.

Soils with a high water holding capacity ab-sorb large amounts of water, minimizing the po-tential for runoff and erosion and storing waterfor use during droughts. Soils are able to absorband hold water when they have a thick soil pro-file; contain a relatively high percentage of or-ganic matter; and do not have a rocky or com-pacted soil layer, such as a hardpan or plowpan,close to the soil surface. An active population ofsoil organisms enhances the formation of aggre-gates and of burrowing channels that providepathways for water to flow into and through thesoil. Management practices that enhance waterinfiltration and water holding capacity include:• a complete coverage of forages and residues

over the soil surface• an accumulation of organic matter in and on

the soil• an active community of soil organisms in-

volved in organic matter decomposition andaggregate formation

• water runoff and soil erosion prevention• protection against soil compaction

SOIL SATURATION

Soils become saturated when the amount of wa-ter entering exceeds the rate of absorption ordrainage. A rocky or compacted lower soil layerwill not allow water to drain or pass through,while a high water table prevents water fromdraining through the profile. Water soaking intothese soils is trapped or perched above the hard

Rainfall

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Subsurface flow

Leachednutrients

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Uptakeby wells


Artificial drainage practices are often usedon soils with a hardpan or a high water table todecrease the duration of soil saturation follow-ing rainfalls or snowmelts. This practice can in-crease water infiltration and decrease the poten-tial for water runoff (5). Unfortunately, most sub-surface drains were installed before water pollu-tion from agriculture became a concern and thusempty directly into drainage ways. Nutrients,pathogens, and other contaminants on the soilsurface can move through large cracks or chan-nels in the soil to drainage pipes where they arecarried to surface water bodies (6).

SOIL COMPACTION

Soil compaction occurs when animals orequipment move across soils that are wet or satu-rated, with moist soils being more easily com-pacted than saturated soils (7). Compaction canalso occur when animals or equipment continu-ally move across a laneway or stand around wa-tering tanks and headlands or under shade. Ani-mals trampling over the ground press down onsoils, squeezing soil pore spaces together. Tram-pling also increases the potential for compactionby disturbing and killing vegetation.

Soils not covered by forages or residues areeasily compacted by the impact of raindrops.When raindrops fall on bare soil, their force causesfine soil particles to splash or disperse. Thesesplash particles land on the soil surface, clog sur-

face soil pores,and form a crustover the soil.Clayey soils aremore easily com-pacted than sandysoils because clayparticles are verysmall and sticky.

Compact ionlimits root growth

and the movement of air, water, and dissolvednutrients through the soil. Compressing andclogging soil surface pores also decreases waterinfiltration and increases the potential for runoff.The formation of hardpans, plowpans, trafficpans, or other compacted layers decreases down-ward movement of water through the soil, caus-ing rapid soil saturation and the inability of soilsto absorb additional water. Compaction in pas-

tures is remediated by root growth, aggregateformation, and activities of burrowing soil organ-isms. In colder climates, frost heaving is an im-portant recovery process for compacted soils (8).

RUNOFF AND EROSION

Runoff water dissolves nutrients and removesthem from the pasture as it flows over the soilsurface. Soil erosion transports nutrients and anycontaminants, such as pesticides and pathogens,attached to soil particles. Because nutrient-richclay and organic matter particles are small andlightweight, they are more readily picked up andmoved by water than the nutrient-poor, butheavier, sand particles. Besides depleting pas-tures of nutrients that could be used for forageproduction, runoff water and erosion carry nu-trients and sediments that contaminate lakes,streams, and rivers.

Landscape condi-tions and manage-ment practices thatfavor runoff and ero-sion include slopingareas, minimal soilprotection by forage or residues, intense rainfall,and saturated soils. While pasture managersshould strive to maintain a complete forage coverover the soil surface, this is not feasible in prac-tice because of plant growth habits and land-scape characteristics. Plant residues from die-back and animal wastage during grazing providea critical source of soil cover and organic matter.As mentioned above, forage type affects waterinfiltration and runoff. Forages with deep rootsenhance water infiltration while plants with a widevegetative coverage area or prostrate growth pro-vide good protection against raindrop impact.Sod grasses that are short-lived and shallow-rooted inhibit water infiltration and encouragerunoff. Grazing practices that produce clumpsof forages separated by bare ground enhance run-off potential by producing pathways for waterflow.

Runoff water and ero-sion carry nutrientsand sediments thatcontaminate lakes,streams, and rivers.

EVAPORATION AND TRANSPIRATION

Water in the soil profile can be lost throughevaporation, which is favored by high tempera-tures and bare soils. Pasture soils with a thickcover of grass or other vegetation lose little wa-ter to evaporation since the soil is shaded andsoil temperatures are decreased. While evapo-

Animals trampling overthe ground press downon soils, squeezing soilpores together, whichlimits root growth andthe movement of air,water, and dissolvednutrients.


ration affects only the top few inches of pasturesoils, transpiration can drain water from the en-tire soil profile. Transpiration is the loss of wa-ter from plants through stomata in their leaves.Especially on sunny and breezy days, significantamounts of water can be absorbed from the soilby plant roots, taken up through the plant, andlost to the atmosphere through transpiration. Adiversity of forage plants will decrease transpi-ration losses and increase water-use efficiency.

This is because forage species differ in their abil-ity to extract water from the soil and conserve itagainst transpiration (9). Some invasive plantspecies, however, can deplete water storesthrough their high water use (4). Water not usedfor immediate plant uptake is held within the soilprofile or is transported to groundwater reserves,which supply wells with water and decrease theimpacts of drought.

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If you answer no to all the questions, you have soils with high water-use efficiency. Ifyou answer yes to some of the questions, water cycle efficiency of your soil will likelyrespond to improved pasture management practices. See Table 2, next page.

Water infiltration / Water runoff

1. Do patches of bare ground separate forage coverage?

2. Are shallow-rooted sod grasses the predominant forage cover?

3. Can you see small waterways during heavy rainfalls or sudden snowmelts?

4. Are rivulets and gullies present on the land?

Soil saturation

5. Following a rainfall, is soil muddy or are you able to squeeze water

out of a handful of soil?

6. Following a rainfall or snowmelt, does it take several days before the

soil is no longer wet and muddy?

7. Do forages turn yellow or die during wet weather?

Soil compaction

8. Do you graze animals on wet pastures?

9. Are some soils in the pasture bare, hard, and crusty?

10. Do you have difficulty driving a post into (non-rocky) soils?

Water retention /Water evaporation and transpiration

11. Do you have a monoculture of forages or are invasive species prominent

components of the pasture?

12. Do soils dry out quickly following a rainstorm?

13. During a drought, do plants dry up quickly?

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YES NO


Ensure forage and residue coverage across the entire pasture• Use practices that encourage animal movement throughout the pasture and discourage con-

gregation in feeding and lounging areas• Use practices that encourage regrowth of forage plants and discourage overgrazing• Use a variety of forages with a diversity of root systems and growth characteristics

Pasture management during wet weather• Use well-drained pastures or a “sacrificial pasture” that is far from waterways or water bodies• Avoid driving machinery on pastures that are wet or saturated• Avoid spreading manure or applying fertilizers

Artificial drainage practices• Avoid grazing animals on artificially drained fields when drains are flowing• Avoid spreading manure or applying fertilizers when drains are flowing• Ensure that drains empty into a filter area or wetland rather than directly into a stream or

drainage way

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Effective carbon cycling in pastures depends on a diversity of plants and healthy populations ofsoil organisms. Plants form carbon and water into carbohydrates through photosynthesis. Plants aremost able to conduct photosynthesis when they can efficiently capture solar energy while also havingadequate access to water, nutrients, and air. Animals obtain carbohydrates formed by plants whenthey graze on pastures or eat hay or grains harvested from fields. Some of the carbon and energy inplant carbohydrates is incorporated into animal cells. Some of the carbon is lost to the atmosphere ascarbon dioxide, and some energy is lost as heat, during digestion and as the animal grows and breathes.

Carbohydrates and other nutrients not used by animals are re-turned to the soil in the form of urine and manure. These organicmaterials provide soil organisms with nutrients and energy. As soilorganisms use and decompose organic materials, they release nutri-ents from these materials into the soil. Plants then use the released,inorganic forms of nutrients for their growth and reproduction. Soilorganisms also use nutrients from organic materials to produce sub-

stances that bind soil particles into aggregates. Residues of organic matter that resist further decom-position by soil organisms form soil humus. This stable organic material is critical for maintaining soiltilth and enhancing the ability of soils to absorb and hold water and nutrients.

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Humus maintains soiltilth and enhances waterand nutrient absorption.

CARBOHYDRATE FORMATION

For productive growth, plants need to effec-tively capture solar energy, absorb carbon diox-ide, and take up water from the soil to producecarbohydrates through photosynthesis. In pas-tures, a combination of broadleaf plants andgrasses allows for efficient capture of solar en-

ergy by a diversity of leaf shapes and leaf angles.Taller plants with more erect leaves capture lighteven at the extreme angles of sunrise and sunset.Horizontal leaves capture the sun at midday orwhen it is more overhead.

Two methods for transforming carbon intocarbohydrates are represented in diversified pas-


tures. Broadleaf plants and cool-season grasseshave a photosynthetic pathway that is efficientin the production of carbohydrates but is sensi-tive to dry conditions. Warm-season grasseshave a pathway that is more effective in produc-ing carbohydrates during hot summer condi-tions. A combination of plants representing thesetwo pathways ensures effective forage growththroughout the growing season. A diversity ofroot structures also promotes photosynthesis bygiving plants access to water and nutrientsthroughout the soil profile.

ORGANIC MATTER DECOMPOSITION

Pasture soils gain organic matter from growthand die-back of pasture plants, from forage wast-age during grazing, and from manure deposition.In addition to the recycling of aboveground plantparts, every year 20 to 50% of plant root massdies and is returned to the soil system. Somepasture management practices also involve theregular addition of manurefrom grazing animals housedduring the winter or from poul-try, hog, or other associatedlivestock facilities.

A healthy and diversepopulation of soil organisms isnecessary for organic matterdecomposition, nutrient miner-alization, and the formation of soil aggregates.Species representing almost every type of soilorganism have roles in the breakdown of manure,plant residues, and dead organisms. As they usethese substances for food and energy sources,

they break down complex carbohydrates and pro-teins into simpler chemical forms. For example,soil organisms break down proteins into carbondioxide, water, ammonium, phosphate, and sul-fate. Plants require nutrients to be in this sim-pler, decomposed form before they can use themfor their growth.

To effectively decompose organic matter, soilorganisms require access to air, water, and nu-trients. Soil compaction and saturation limit thegrowth of beneficial organisms and promote thegrowth of anaerobic organisms, which are inef-ficient in the decomposition of organic matter.These organisms also transform some nutrientsinto forms that are less available or unavailableto plants. Nutrient availability and nutrient bal-ances in the soil solution also affect the growthand diversity of soil organisms. To decomposeorganic matter that contains a high amount ofcarbon and insufficient amounts of other nutri-ents, soil organisms must mix soil- solution nu-

trients with this material toachieve a balanced diet.

Balances between theamount of carbon and nitro-gen (C:N ratio) and theamount of carbon and sulfur(C:S ratio) determinewhether soil organisms willrelease or immobilize nutri-

ents when they decompose organic matter. Im-mobilization refers to soil microorganisms takingnutrients from the soil solution to use in the de-composition process of nutrient-poor materials.Since these nutrients are within the bodies of soil

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The Carbon Cycle begins with plants taking up carbondioxide from the atmosphere in the process of photosynthesis.Some plants are eaten by grazing animals, which returnorganic carbon to the soil as manure, and carbon dioxide tothe atmosphere. Easily broken-down forms of carbon inmanure and plant cells are released as carbon dioxide whendecomposing soil organisms respire. Forms of carbon thatare difficult to break down become stabilized in the soil ashumus.

A healthy and diverse popu-lation of soil organisms isnecessary for organic matterdecomposition, nutrient min-eralization, and the formationof soil aggregates.


organisms, they are temporarily unavailable toplants. In soils with low nutrient content, thiscan significantly inhibit plant growth. However,immobilization can be beneficial in soils with ex-cess nutrients. This process conserves nutrientsin bodies of soil organisms, where they are lesslikely to be lost through leaching and runoff (10).

Populations of soil organisms are enhancedby soil that is not com-pacted and has adequateair and moisture, andby additions of freshresidues they canreadily decompose.Soil-applied pesticidescan kill many beneficialsoil organisms, as willsome chemical fertiliz-ers. Anhydrous ammo-nia and fertilizers witha high chloride content, such as potash, are par-ticularly detrimental to soil organisms. Moder-ate organic or synthetic fertilizer additions, how-ever, enhance populations of soil organisms insoils with low fertility.

SOIL HUMUS AND SOIL AGGREGATES

Besides decomposing organic materials, bac-teria and fungi in the soil form gels and threadsthat bind soil particles together. These boundparticles are called soil aggregates. Worms,beetles, ants, and other soil organisms move par-tially decomposed organic matter through the soilor mix it with soil in their gut, coating soil par-ticles with organic gels. As soil particles become

In soils with low nutrient con-tent, nutrient immobilizationinhibits plant growth. In soilswith excess nutrients, immo-bilization conserves nutrientsin the bodies of soil organ-isms, where they are lesslikely to be lost through leach-ing and runoff.

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%N C:N %S C:S N:SDead grass 1.8 26.6:1 0.15 320:1 12:1Dead clover 2.7 17.7:1 0.18 270:1 15:1Grass roots 1.4 35:1 0.15 330:1 9:1Clover roots 3.8 13.2:1 0.35 140:1 10:1Cattle feces 2.4 20:1 0.30 160:1 8:1Cattle urine 11.0 3.9:1 0.65 66:1 17:1Bacteria 15.0 3.3:1 1.1 45:1 14:1Fungi 3.4 12.9:1 0.4 110:1 8.5:1

Typical C:N, C:S, and N:S ratios of plant residues, excreta of ruminant animals, and biomass of soilmicroorganisms decomposing in grassland soils (based on values for % in dry matter)

From Whitehead, 2000 (reference #11)

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

aggregated, soil pore size increases and soils be-come resistant to compaction. The organic com-pounds that hold aggregates together also in-crease the ability of soils to absorb and hold wa-ter and nutrients.

As soil organisms decompose manure andplant residues, they release carbon dioxide andproduce waste materials, which are further de-

composed by other soil organisms. Be-cause carbon is lost to respiration ateach stage of this decomposition pro-cess, the remaining material increasesin relative nitrogen content. The re-maining material also increases inchemical complexity and requires in-creasingly specialized species of de-composers. Efficient decompositionof organic matter thus requires a di-versity of soil organisms. Humus isthe final, stable product of decompo-

sition, formed when organic matter can be bro-ken down by soil organisms only slowly or withdifficulty. Humus-coated soil particles form ag-gregates that are soft, crumbly, and somewhatgreasy-feeling when rubbed together.

PREVENTING ORGANIC MATTER LOSSES

Perennial plant cover in pastures not onlyprovides organic matter inputs, it also protectsagainst losses of organic matter through erosion.Soil coverage by forages and residues protectsthe soil from raindrop impact while dense rootsystems of forages hold the soil against erosionwhile enhancing water infiltration. Fine root hairsalso promote soil aggregation. In addition, a


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dense forage cover shades and cools the soil. High temperatures promote mineralization and loss oforganic matter, while cooler temperatures promote the continued storage of this material within the plantresidues and the bodies of soil organisms.

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Ensure forage and residue coverage and manure deposition across the entire pasture• Use practices that encourage animal movement throughout the pasture and discourage con-

gregation in feeding and lounging areas

Promote healthy forage growth and recovery following grazing• Use a variety of forages with a diversity of leaf types and orientations• Use a combination of cool- and warm-season forages with a diversity of shoot and root growth

characteristics• Conserve sufficient forage leaf area for efficient plant regrowth by monitoring pastures and

moving grazing animals to another pasture in a timely manner• Maintain soil tilth for healthy root growth and nutrient uptake

Encourage organic matter decomposition by soil organisms• Use management practices that minimize soil compaction and soil erosion• Minimize tillage and other cultivation practices• Maintain a diversity of forage species to provide a variety of food sources and habitats for a

diversity of soil organisms• Avoid the use of soil-applied pesticides and concentrated fertilizers that may kill or inhibit the

growth of soil organisms

Encourage soil humus and aggregate formation• Include forages with fine, branching root systems to promote aggregate formation• Maintain organic matter inputs into the soil to encourage the growth of soil organisms• Maintain coverage of forages and plant residues over the entire paddock to provide organic

matter and discourage its rapid degradation

Nitrogen is a primary plant nutrient and amajor component of the atmosphere. In a pas-ture ecosystem, almost all nitrogen is organicallybound. Of this, only about 3% exists as part of aliving plant, animal, or microbe, while the re-mainder is a component of decomposed organicmatter or humus. A very small percentage ofthe total nitrogen (less than 0.01%) exists as plant-available nitrogen in the form of ammonium ornitrate (12).

Nitrogen becomes available for the growthof crop plants and soil organisms through nitro-gen fixation, nitrogen fertilizer applications, the

return of manure to the land, and through themineralization of organic matter in the soil. Ni-trogen fixation occurs mainly in the roots of le-gumes that form a symbiotic association with atype of bacteria called rhizobia. Some free-livingbacteria, particularly cyanobacteria (“blue-greenalgae”), are also able to transform atmosphericnitrogen into a form available for plant growth.Fertilizer factories use a combination of highpressure and high heat to combine atmosphericnitrogen and hydrogen into nitrogen fertilizers.Animals deposit organically-bound nitrogen infeces and urine. Well-managed pastures accu-


The Nitrogen Cycle. Nitrogen enters the cycle whenatmospheric nitrogen is fixed by bacteria. Nitrogen in theammonical form is transformed into nitrite and nitrate bybacteria. Plants can use either ammonia or nitrate forgrowth. Nitrogen in plant cells can be consumed by animalsand returned to the soil as feces or urine. When plants die,soil organisms decompose nitrogen in plant cells and releaseit as ammonia. Nitrate nitrogen can be lost through thephysical process of leaching or through the microbially-mediated process of denitrification. Nitrogen in theammonical form can be lost to the atmosphere in thechemical process of volatilization.

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#N/acre/ yearAlfalfa -------------------------------------- 150-350White clover ------------------------------ 112-190Hairy vetch ------------------------------- 110-168Red clover --------------------------------- 60-200Soybeans ---------------------------------- 35-150Annual lespedeza ----------------------- 50-193Birdsfoot trefoil --------------------------- 30-130

From Joost, 1996 (Reference # 13)

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mulate stores of organic matter in the soil and inplant residues. Decomposition and mineraliza-tion of nutrients in these materials can providesignificant amounts of nitrogen to plants andother organisms in the pasture system.

Plants use nitrogen for the formation of pro-teins and genetic material. Grazing animals thatconsume these plants use some of the nitrogenfor their own growth and reproduction; the re-mainder is returned to the earth as urine or ma-nure. Soil organisms decompose manure, plantresidues, dead animals, and microorganisms,transforming nitrogen-containing compounds intheir bodies into forms that are available for useby plants.

Nitrogen is often lacking in pasture systemssince forage requirements for this nutrient arehigh and because it is easily lost to the environ-ment. Nitrogen is lost from pasture systemsthrough microbiological, chemical, and physicalprocesses. Dry followed by wet weather pro-vides optimal conditions for bacteria to transformnitrogen from plant-available forms into atmo-spheric nitrogen through denitrification. Chemi-cal processes also transform plant-available ni-trogen into atmospheric nitrogen through vola-tilization. In pastures, this often occurs after ma-nure or nitrogen fertilizers are applied to the soilsurface, especially during warm weather. Physi-cal processes are involved in the downwardmovement of nitrogen through the soil profileduring leaching.

NITROGEN FIXATION

Plants in the legume family, including alfalfa,clover, lupines, lespedeza, and soybeans, form arelationship with a specialized group of bacteriacalled rhizobia. These bacteria have the ability tofix or transform atmospheric nitrogen into a formof nitrogen plants can use for their growth.Rhizobia form little balls or nodules on the rootsof legumes. If these balls are white or pinkishon the inside, they are actively fixing nitrogen.Nodules that are grey or black inside are dead orno longer active. Legume seeds should be dustedwith inoculum (a liquid or powder containingthe appropriate type of rhizobia) prior to plant-ing to ensure that the plant develops many nod-ules and has maximal ability to fix nitrogen.Other microorganisms that live in the soil are alsoable to fix and provide nitrogen to plants.


Legumes can transferup to 40% of their fixednitrogen to grassesduring the growingseason.

Legumes require higher amounts of phospho-rus, sulfur, boron, and molybdenum than non-legumes to form nodules and fix nitrogen. If thesenutrients are not available in sufficient amounts,nitrogen fixation will be suppressed. When ni-trogen levels in the soil are high due to applica-tions of manure or nitrogen fertilizers, nitrogenfixation by legumes decreases because nitrogenfixation requires more energy than does root up-take of soluble soil nitrogen. Nitrogen fixed bylegumes and rhizobia is available primarily to thelegumes while they are growing. When pasturelegume nodules, root hairs, and abovegroundplant material dies and decomposes, nitrogen inthis material can become available to pasturegrasses (14).

However, while legumes are still growing,mycorrhizal fungi can form a bridge between theroot hairs of legumes and nearby grasses. Thisbridge facilitates the transport of fixed nitrogenfrom legumes to linked grasses. Depending on

the nitrogen con-tent of the soil andthe mix of legumesand grasses in apasture, legumescan transfer be-tween 20 and 40%of their fixed nitro-

gen to grasses during the growing season (15).A pasture composed of at least 20 to 45% legumes(dry matter basis) can meet and sustain the ni-trogen needs of the other forage plants in the pas-ture (16).

Grazing management affects nitrogen fixationthrough the removal of herbage, deposition ofurine and manure, and induced changes in mois-ture and temperature conditions in the soil. Re-moval of legume leaf area decreases nitrogen fixa-tion by decreasing photosynthesis and plant com-petitiveness with grasses. Urine deposition de-creases nitrogen fixation by adjacent plants sinceit creates an area of high soluble-nitrogen avail-ability. Increased moisture in compacted soilsor increased temperature in bare soils will alsodecrease nitrogen fixation since rhizobia are sen-sitive to wet and hot conditions.

NITROGEN MINERALIZATION

Decomposition of manure, plant residues, orsoil organic matter by organisms in the soil re-

sults in the formation of ammonia. Protozoa,amoebas, and nematodes are prolific nitrogenmineralizers, cycling 14 times their biomass eachyear. While bacteria only cycle 0.6 times theirbiomass, because of their large numbers in soilthey produce a greater overall contribution to thepool of mineralized nitrogen (17). Plants can useammonical nitrogen for their growth, but underaerobic conditions two types of bacteria usuallywork together to rapidly transform ammonia firstinto nitrite and then into nitrate before it is usedby plants.

Mineralization is a very important source ofnitrogen in most grasslands. As discussed above,for efficient decomposition (and release of nitro-gen), residues must contain a carbon-to-nitrogenratio that is in balance with the nutrient needs ofthe decomposer organisms. If the nitrogen con-tent of residues is insufficient, soil organisms willextract nitrogen from the soil solution to satisfytheir nutrient needs.

NITROGEN LOSSES TO THE ATMOSPHERE

Under wet or anaerobic conditions, bacteriatransform nitrate nitrogen into atmospheric ni-trogen. This process, called denitrification, re-duces the availability of nitrogen for plant use.Denitrification occurs when dry soil containingnitrate becomes wet or flooded and at the edgesof streams or wetlands where dry soils are adja-cent to wet soils.

Volatilization is the transformation of ammo-nia into atmospheric nitrogen. This chemicalprocess occurs when temperatures are high andammonia is exposed to the air. Incorporation ofmanure or ammonical fertilizer into the soil de-creases the potential for volatilization. In gen-eral, 5 to 25% of the nitrogen in urine is volatil-ized from pastures (11). A thick forage cover andrapid manure decomposition can reduce volatil-ization from manure.

NITROGEN LEACHING

Soil particles and humus are unable to holdnitrate nitrogen very tightly. Water from rainfallor snowmelt readily leaches soil nitrate down-ward through the profile, putting it out of reachof plant roots or moving it into the groundwater.Leaching losses are greatest when the water tableis high, the soil sandy or porous, or when rainfallor snowmelt is severe. In pastures, probably themost important source of nitrate leaching is from


urine patches (18). Cattle urine typically leaches toa depth of 16 inches, while sheep urine leaches onlysix inches into the ground (19). Leaching may alsobe associated with the death of legume nodulesduring dry conditions (20).

Methods for reducing nitrate leaching includemaintaining an actively growing plant cover overthe soil surface, coordinating nitrogen applicationswith the period of early plant growth, not applyingexcess nitrogen to soils, and encouraging animalmovement and distribution of manure across pad-docks. Actively growing plant roots take up ni-trate from the soil and prevent it from leaching. Ifthe amount of nitrogen applied to the soil is in ex-cess of what plants need or is applied when plantsare not actively growing, nitrate not held by plantscan leach through the soil. Spring additions of ni-trogen to well-managed pastures can cause exces-sive plant growth and increase the potential forleaching. This is because significant amounts ofnitrogen are also being mineralized from soil or-ganic matter as warmer temperatures increase theactivity of soil organisms.

Nitrate levels in excess of 10 ppm in drinkingwater can cause health problems for human infants,infant chickens and pigs, and both infant and adultsheep, cattle, and horses (21). Pasture forages canalso accumulate nitrate levels high enough to causehealth problems. Conditions conducive for nitrateaccumulation by plants include acid soils; low mo-lybdenum, sulfur, and phosphorus content; soiltemperatures lower than 550 F; and good soil aera-tion (22).

Nitrate poisoning is called methemoglobinemia,commonly known as “blue baby syndrome” whenseen in human infants. In this syndrome, nitratebinds to hemoglobin in the blood, reducing theblood’s ability to carry oxygen through the body.Symptoms in human infants and young animalsinclude difficulty breathing. Pregnant animals thatrecover may abort within a few days. Personnelfrom the Department of Health can test wells todetermine whether nitrate levels are dangerouslyhigh.

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From Whitehead, 2000 (Reference # 11)

Moderately managed Extensively grazedgrass-clover grass

Inputs

Nitrogen fixation 134 9 Atmospheric deposition 34 19 Fertilizer 0 0 Supplemental feed 0 0

Recycled nutrients

Uptake by herbage 270 67 Herbage consumption by animals 180 34 Dead herbage to soil 90 34 Dead roots to soil 56 34 Manure to soil 134 28

Outputs

Animal weight gain 28 4 Leaching/runoff/erosion 56 6 Volatilization 17 3 Denitrification 22 2

Gain to soil 56 13


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Ensure effective nitrogen fixation by legumes

• Ensure that phosphorus, sulfur, boron, and molybdenum in the soil are sufficient foreffective nitrogen fixation

• Apply inoculum to legume seeds when sowing new pastures to ensure nodulation oflegume roots

• Ensure that legumes represent at least 30% of the forage cover• Maintain stable or increasing ratios of legumes to grasses and other non-legumes in

pastures over time• Establish forages so that legumes and grasses grow close to one another to allow for

the transfer of nitrogen from legumes to grasses

Encourage nitrogen mineralization by soil organisms

• Use management practices that minimize soil compaction and soil erosion• Minimize tillage and other cultivation practices• Maintain a diversity of forage species to provide a variety of food sources and habitats

for a diversity of soil organisms• Use grazing management practices that encourage productive forage growth and that

return and maintain residues within paddocks• Avoid application of sawdust, straw, or other high-carbon materials unless these mate-

rials are mixed with manure or composted prior to application• Avoid the use of soil-applied pesticides and concentrated fertilizers that may kill or

inhibit the growth of soil organisms

Avoid nitrogen losses

• Minimize nitrogen volatilization by avoiding surface application of manure, especiallywhen the temperature is high or there is minimal forage cover over the soil

• Minimize nitrogen leaching by not applying nitrogen fertilizer or manure when soil iswet or just prior to rainstorms and by encouraging animal movement and distribution ofurine spots across paddocks

• Minimize nitrogen leaching by not applying nitrogen fertilizer or manure to sandy soilsexcept during the growing season

• Rely on mineralization of organic residues to supply most or all of your forage nitrogenneeds in the spring. Minimize the potential for nitrogen leaching by limiting springapplications of nitrogen

• Minimize nitrogen losses caused by erosion by using management practices that main-tain a complete cover of forages and residues over the pasture surface

Ensure effective use of nitrogen inputs

• Use management practices that encourage the even distribution of manure and urineacross paddocks

• Rely on soil tests and other nutrient management practices when applying fertilizersand manure to pastures


NITROGEN LOSS THROUGH

RUNOFF AND EROSION

Runoff and erosion caused by rainwater orsnowmelt can transport nitrogen on the soil sur-face. Erosion removes soil particles and organicmatter containing nitrogen; runoff transports dis-solved ammonia and nitrate. Incorporation ofmanure and fertilizers into the soil reduces theexposure of these nitrogen sources to rainfall orsnowmelt, thus reducing the potential for ero-sion. In pasture systems, however, incorpora-tion is usually impractical and can increase thepotential for erosion. Instead, a complete cover

The Phosphorus Cycle is affected by microbial andchemical transformations. Soil organisms mineralize orrelease phosphorus from organic matter. Phosphorus ischemically bound to iron and aluminum in acid soils, andto calcium in alkaline soils. Soil-bound phosphorus can belost through erosion, while runoff waters can transportsoluble phosphorus found at the soil surface.

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of forages and plant residues should be main-tained over the soil surface to minimize raindropimpact on the soil, enhance water infiltration,help trap sediments and manure particles, andreduce the potential for runoff and erosion. Ahealthy and diverse population of soil organisms,including earthworms and dung beetles that rap-idly incorporate manure nitrogen into the soiland into their cells, can further reduce the risk ofnitrogen runoff from manure. Since increasedwater infiltration decreases the potential for run-off but increases the potential for leaching, risksof nitrate losses from runoff need to be balancedagainst leaching risks.

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Like nitrogen, phosphorus is a primary plant nutrient. Unlike nitrogen, phosphorus is not part ofthe atmosphere. Instead, it is found in rocks, minerals, and organic matter in the soil. The mineralforms of phosphorus include apatitite (which may be in a carbonate, hydroxide, fluoride, or chlorideform) and iron or aluminum phosphates. These minerals are usually associated with basalt and shalerocks. Chemical reactions and microbial activity affect the availability of phosphorus for plant up-take. Under acid conditions, phosphorus is held tightly by aluminum and iron in soil minerals.Under alkaline conditions, phosphorus is held tightly by soil calcium.

Plants use phosphorus for energy transfer and reproduction. Legumes require phosphorus foreffective nitrogen fixation. Animals consume phosphorus when they eat forages. Phosphorus notused for animal growth is returned to the soil in manure. Following decomposition by soil organ-isms, phosphorus again becomes available for plant uptake.


MYCORRHIZAE

Mycorrhizal fungi attach to plant roots andform thin threads that grow through the soil andwrap around soil particles. These thin threadsincrease the ability of plants to obtain phospho-rus and water from soils. Mycorrhizae are espe-cially important in acid and sandy soils wherephosphorus is either chemically bound or haslimited availability. Besides transferring phos-phorus and water from the soil solution to plantroots, mycorrhizae also facilitate the transfer ofnitrogen from legumes to grasses. Well aeratedand porous soils, and soil organic matter, favormycorrhizal growth.

SOIL CHEMISTRY AND

PHOSPHORUS AVAILABILITY

Phosphorus is tightly bound chemically inhighly weathered acid soils that contain high con-centrations of iron and aluminum. Active cal-cium in neutral to alkaline soils also forms tightbonds with phosphorus. Liming acid soils andapplying organic matter to either acid or alka-line soils can increase phosphorus availability.In most grasslands, the highest concentration ofphosphorus is in the surface soils associated withdecomposing manure and plant residues.

PHOSPHORUS LOSS THROUGH

RUNOFF AND EROSION

Unlike nitrogen, phosphorus is held by soilparticles. It is not subject to leaching unless soillevels are excessive. However, phosphorus canmove through cracks and channels in the soil toartificial drainage systems, which can transportit to outlets near lakes and streams. Dependingon the soil type and the amount of phosphorusalready in the soil, phosphorus added as fertil-

izer or manure may be readily lost from fieldsand transported to rivers and streams throughrunoff and erosion. The potential for phospho-rus loss through runoff or erosion is greatestwhen rainfall or snowmelt occurs within a fewdays following surface applications of manureor phosphorus fertilizers.

Continual manure additions increase the po-tential for phosphorus loss from the soil and thecontamination of lakes and streams. This is es-pecially true if off-farm manure sources are usedto meet crop or forage nutrient needs for nitro-gen. The ratio of nitrogen to phosphate in swineor poultry manure is approximately 1 to 1, whilethe ratio of nitrogen to phosphate taken up byforage grasses is between 2.5 to 1 and 3.8 to 1.Thus, manure applied for nitrogen requirementswill provide 2.5 to 3.8 times the amount of phos-phorus needed by plants (23). While much ofthis phosphorus will be bound by chemicalbonds in the soil and in the microbial biomass,continual additions will exceed the ability of thesoil to store excess phosphorus, and the amountof soluble phosphorus (the form available for lossby runoff) will increase. To decrease the poten-tial for phosphorus runoff from barnyard manureor poultry litter, alum or aluminum oxide can beadded to bind phosphorus in the manure (24).

Supplemental feeds are another source ofphosphorus inputs to grazing systems, especiallyfor dairy herds. Feeds high in phosphorus in-crease the amount of phosphorus deposited onpastures as manure. To prevent build up of ex-cess phosphorus in the soil, minimize feeding ofunneeded supplements, conduct regular soil testson each paddock, and increase nutrient remov-als from excessively fertile paddocks throughhaying.

Phosphorus runoff from farming operationscan promote unwanted growth of algae in lakesand slow-moving streams. Regulations andnutrient-management guidelines are being de-veloped to decrease the potential for phospho-rus movement from farms and thus reduce risksof lake eutrophication. Land and animal man-agement guidelines, called “phosphorus indi-ces,” are being developed across the U.S. to pro-vide farmers with guidelines for reducing “non-point” phosphorus pollution from farms (25).These guidelines identify risk factors for phos-phorus transport from fields to water bodiesbased on the concentration of phosphorus in the


Phosphorus index guidelines consider:• the amount of phosphorus in the soil• manure and fertilizer application rates, methods, and timing• runoff and erosion potential• distance from a water body

Encourage phosphorus mineralization by soil organisms• Use management practices that minimize soil compaction and soil erosion• Minimize use of tillage and other cultivation practices• Maintain a diversity of forage species to provide a variety of food sources and habitats

for a diversity of soil organisms• Avoid application of sawdust, straw, or other high-carbon materials unless these materi-

als are mixed with manure or composted prior to application• Avoid the use of soil-applied pesticides and concentrated fertilizers that may kill or inhibit

the growth of soil organisms

Avoid phosphorus losses• Minimize phosphorus losses caused by erosion by using management practices that

maintain a complete cover of forages and residues over the pasture surface• Minimize phosphorus losses caused by runoff by not surface-applying fertilizer or ma-

nure to soil that is saturated, snow-covered, or frozen• Avoid extensive grazing of animals in or near streams especially when land is wet or

saturated or when streams are at low flow

Ensure effective use of phosphorus inputs• Use management practices that encourage the even distribution of manure and urine

across paddocks• Rely on soil tests, phosphorus index guidelines, and other nutrient management prac-

tices when applying fertilizers and manure to pastures

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soil, timing and method of fertilizer and manureapplications, potential for runoff and erosion, anddistance of the field from a water body (26). Al-though the total amount of phosphorus lost fromfields is greatest during heavy rainstorms, snow-melts, and other high-runoff events, relativelysmall amounts of phosphorus running off fromfields into streams at low water level in summerpose a higher risk for eutrophication. This is be-cause phosphorus is more concentrated in thesesmaller flows of water (27). Conditions for con-centrated flows of phosphorus into low-flow

streams include location near streams of barn-yards or other holding areas without runoff con-tainment or filtering systems, extensive grazingof animals near streams without riparian buff-ers, and unlimited animal access to streams.


Potassium and the secondary nutrients, cal-cium, magnesium, and sulfur, play a critical rolein plant growth and animal production. Potas-sium, calcium, and magnesium are componentsof clay minerals. The soil parent-material pri-marily influences the availability of these plantnutrients. For example, soils derived from gran-ite contain, on the average, nine times more po-tassium than soils derived from basalt, while soilsderived from limestone have half the amount.Conversely, soils derived from limestone have,on the average, four times more calcium thansoils derived from basalt and thirty times morethan soils derived from granite (11).

POTASSIUM

Potassium, like all plant nutrients, is recycledthrough plant uptake, animal consumption, andmanure deposition. The majority of potassiumis found in urine. Potassium levels can becomeexcessive in fields that have received repeatedhigh applications of manure. Application of fer-tilizer nitrogen increases the potassium uptakeby grasses if the soil has an adequate supply ofpotassium. Consumption of forages that containmore than 2% potassium can cause problems inbreeding dairy cattle and in their recovery fol-lowing freshening (28). High potassium levels,especially in lush spring forage, can cause nutri-ent imbalance resulting in grass tetany.

CALCIUM AND MAGNESIUM

Calcium and magnesium are components ofliming materials used to increase soil pH and re-duce soil acidity. However, the use of lime canalso be important for increasing the amount ofcalcium in the soil or managing the balance be-tween calcium and magnesium. Increasing thecalcium concentration may enhance biological ac-tivity in the soil (29). Managing this balance isespecially important for decreasing the occur-rence of grass tetany, a nutritional disorder ofruminants caused by low levels of magnesiumin the diet. Magnesium may be present in thesoil in sufficient amounts for plant growth, butits concentration may be out of balance with thenutrient needs of plants and animals. When cal-cium and potassium have a high concentration

in the soil compared to magnesium, they willlimit the ability of plants to take up magnesium.Under these conditions, the magnesium concen-tration needs to be increased relative to calcium.Dolomite lime, which contains magnesium car-bonate, can be used to both lime soils and in-crease the availability of magnesium. Phospho-rus fertilization of tall fescue in Missouri was alsoshown to increase the availability of magnesiumsufficiently to decrease the incidence of grasstetany in cattle (30). This probably resulted fromthe stimulation of grass growth during cool wetspring conditions that are conducive to the oc-currence of grass tetany.

SULFUR

Sulfur increases the protein content of pas-ture grasses and increases forage digestibility andeffectiveness of nitrogen use (31). In nature, sul-fur is contained in igneous rocks, such as graniteand basalt, and is a component of organic mat-ter. In areas downwind from large industrial andurban centers, sulfur contributions from the at-mosphere in the form of acid rain can be consid-erable. Fertilizer applications of nitrogen as am-monium sulfate or as sulfur-coated urea also con-tribute to sulfur concentration in soils. However,pasture needs for sulfur fertilization will increaseas environmental controls for acid rain improve,as other sources of nitrogen fertilizer are used,and as forage production increases.

Microbial processes affect sulfur availability.As with nitrogen, the sulfur content of organicmatter determines whether nutrients will be min-eralized or immobilized. Also as with nitrogen,the sulfur content of grasses decreases as theybecome older and less succulent. Thus, soil or-ganisms will decompose younger plants morerapidly and thereby release nutrients while theywill decompose older plant material more slowly

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Phosphorus fertilization of tall fescuedecreased the incidence of grasstetany in cattle since it stimulated grassgrowth and increased the availabilityof magnesium during cool wet springconditions.


and may immobilize soil nutrients in the processof decomposition.

Chemical and biological processes are involvedin sulfur transformations. In dry soils that becomewet or waterlogged, chemical processes transformsulfur from the sulfate to sulfide form. If these wetsoils dry out or are drained, bacteria transform sul-fide to sulfate. Like nitrate, sulfate is not readilyabsorbed by soil minerals, especially in soils witha slightly acid to neutral pH. As a result, sulfatecan readily leach through soils that are sandy orhighly permeable.

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Encourage nutrient mineralization by soil organisms• Use management practices that minimize soil compaction and soil erosion• Minimize use of tillage and other cultivation practices• Maintain a diversity of forage species to provide a variety of food sources and habitats

for a diversity of soil organisms• Avoid the use of soil-applied pesticides and concentrated fertilizers that may kill or in-

hibit the growth of soil organisms• Encourage animal movement across paddocks for even distribution of manure nutrients

Avoid nutrient losses• Minimize sulfur losses by using management practices that decrease the potential for

leaching• Minimize nutrient losses caused by erosion by using management practices that main-

tain a complete cover of forages and residues over the pasture surface

Maintain nutrient balances in the pasture• Ensure magnesium availability to minimize the potential for grass tetany. This can be

done by balancing the availability of magnesium with the availability of other soil cat-ions, particularly potassium and calcium. Phosphorus fertilization of pastures in springcan also enhance magnesium availability

• Guard against a buildup of potassium in pastures by not overapplying manure. Highpotassium levels can cause reproductive problems, especially in dairy cows


Nutrient balances and nutrient availabilitydetermine the fate of nutrients in pastures. Inthe simplest of grazing sys-tems, forage crops take upnutrients from the soil;haying and grazing removeforage crops and their asso-ciated nutrients; and animalmanure deposition returnsnutrients to the soil. Con-tinual nutrient removals de-plete soil fertility unless fer-tilizers, whether organic orsynthetic, are added to re-plenish nutrients. Nutrients may be added topastures by providing animals with feed supple-ments produced off-farm.

Chemical and biological interactions deter-mine the availability of nutrients for plant use.Both native soil characteristics and land manage-ment practices affect these interactions. Phos-phorus can be held chemically by iron or alumi-num bonds while potassium can be held withinsoil minerals. Practices that erode topsoil anddeplete soil organic matter decrease the abilityof soils to hold or retain nutrients. All crop nu-trients can be components of plant residues orsoil organic matter. The type of organic matteravailable and the activity of soil organisms de-termine the rate and amount of nutrients miner-alized from these materials. Nutrient availabil-ity and balance in forage plants affect the healthof grazing animals. Depleted soils produce un-healthy, low-yielding forages and unthrifty ani-mals; excess soil nutrients can be dangerous toanimal health and increase the potential for con-tamination of wells, springs, rivers, and streams.

source of calcium and magnesium. Some claysoils and soils with high percentages of organic

matter contain a native storeof nutrients in addition tohaving the capacity to holdnutrients added by manure,crop residues, or fertilizers.Soils formed under temper-ate prairies or in flood plainshave built up fertilitythrough a long history of or-ganic matter deposition andnutrient accumulation.Sandy soils and weathered,

reddish clay soils contain few plant nutrients andhave a limited ability to hold added nutrients.Soils formed under desert conditions are oftensaline, since water evaporating off the soil sur-face draws water in the soil profile upward. Thiswater carries nutrients and salts, which are de-posited on the soil surface when water evapo-rates. Tropical soils generally have low fertilitysince they were formed under conditions of hightemperatures, high biological activity, and highrainfall that caused rapid organic matter decom-position and nutrient leaching.

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Nutrient-depleted soils producelow-yielding forages and unthriftyanimals.

Excess soil nutrients can be dan-gerous to animal health and in-crease the potential for contami-nation of wells, springs, rivers,and streams.

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Chemical, physical, geological, and biologi-cal processes affect nutrient content and avail-ability in soils. As discussed in the previouschapter, soils derived from basalt and shale pro-vide phosphorus to soils, granite contains highconcentrations of potassium, and limestone is a

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Many clay minerals are able to hold ontowater and nutrients and make them available forplant growth. The pH, or level of acidity or al-kalinity of the soil solution, strongly influencesthe strength and type of bonds formed betweensoil minerals and plant nutrients. Soil pH alsoaffects activities of soil organisms involved in thedecomposition of organic matter and the disso-lution of plant nutrients from soil minerals.Many clay soil particles are able to bind largeamounts of nutrients because of their chemicalcomposition and because they are very small andhave a large surface area for forming bonds.Unfortunately, this small size also makes clayparticles prone to compaction, which can reducenutrient and water availability. Sandy soils areporous and allow water to enter the soil rapidly.


But these soils are unable to hold water or nutri-ents against leaching. Organic matter has a highcapacity to hold both nutrients and water. Soilaggregates, formed by plant roots and soil organ-isms, consist of mineral and organic soil compo-nents bound together in soft clumps. Aggregatesenhance soil porosity, facilitate root growth, al-low for better infiltration and movement of wa-ter and nutrients through soil, and help soils re-sist compaction.

Compacted soils do not allow fornormal root growth. This rootgrew horizontally when itencountered a compacted layer.

Animal movement compacts soil pores, es-pecially when soils are wet or saturated. Con-tinual trampling and foraging, especially in con-gregation areas and laneways, also depletes plantgrowth and produces bare spots.

Soil compaction reduces nutrient availabil-ity for plant uptake by blocking nutrient trans-port to roots and restricting root growth throughthe soil profile. Treading and compaction cansubstantially reduce forage yields. One studyshowed that the equivalent of 12 sheep treadingon mixed ryegrass, white clover, and red cloverpasture reduced yields by 25% on dry soil, 30%on moist soil, and 40% on wet soil compared tono treading. On wet soils, root growth was re-duced 23% (35).

Compaction also decreases the rate of organicmatter decomposition by limiting the access soilorganisms have to air, water, or nutrients. In ad-dition, compacted soils limit water infiltration

and increase the potential forwater runoff and soil erosion. InArkansas, observers of over-grazed pastures found that ma-nure piles on or near bare, com-pacted laneways were morereadily washed away by runoffthan were manure piles in morevegetated areas of the pasture(24).

The potential for animals tocause soil compaction increaseswith soil moisture, the weight ofthe animal, the number of ani-mals in the paddock, and theamount of time animals stay inthe paddock. The potential for a

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In pastures, continual removal of nutrientsthrough harvests or heavy grazing without re-turn or addition of nutrients depletes the soil.Land management practices that encourage soilerosion — such as heavy grazing pressure,plowing up and down a slope, or leaving a fieldbare of vegetation during times of heavy rainsor strong winds — also result in depletion ofsoil fertility. Some pasture management prac-tices involve the use of fire to stimulate growthof native forages (32). Burning readily miner-alizes phosphorus, potassium, and other nu-trients in surface crop residues. It also volatil-izes carbon and nitrogen from residues and re-leases these nutrients into the atmosphere, thusminimizing the ability of organic matter to ac-cumulate in the soil. Loss of residues also ex-poses soil to raindrop impact and erosion. Hotuncontrolled fires increase the potential for ero-sion by degrading natural bio-logical crusts formed by li-chens, algae, and other soil or-ganisms, and by promoting theformation of physical crustsformed from melted soil min-erals (33, 34). The continualhigh application of manure,whey, sludge, or other organicwaste products to soils cancause nutrients to build up toexcessive levels. Pasture man-agement practices that influ-ence soil compaction, soil satu-ration, the activity of soil or-ganisms, and soil pH affectboth soil nutrient content andavailability.

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Soil compaction increases as soil mois-ture, animal weight, animal numbers,and the length of stay in the paddock in-crease.

Resistance to compaction increases asforage establishment and the percentageof plants with fibrous roots increase.


paddock to resist compaction depends on the du-ration of forage establishment and the type offorage root system. Established forages withstrong and prolific root growth in the top six to10 inches of the soil profile are able to withstandtreading by grazing animals. Grasses with ex-tensive fibrous root systems, such as bermudagrass, are able to withstand trampling better thangrasses like orchardgrass that have non-branch-ing roots or legumes like white clover that havetaproots (36). Bunch grasses expose more soil toraindrop impact than closely seeded non-bunchgrasses or spreading herbaceous plants. How-ever, these grasses enhance water infiltration bycreating deep soil pores with their roots (3). Com-bining bunch grasses with other plant varietiescan increase water infiltration while decreasingthe potential for soil compaction and water run-off.

The risk of soil compaction can alsobe reduced by not grazing animals onpaddocks that are wet or have poorly-drained soils. Instead, during wet con-ditions, graze animals on paddocks thathave drier soils and are not adjacent tostreams, rivers, seeps, or drainage ways.Soils that are poorly drained should beused only in the summer when the cli-mate and the soil are relatively dry.

Compacted soils can recover from theimpacts of compaction, but recovery is

slow. Periods of wet weather alternating withperiods of dry weather can reduce compactionin some clay soils. Freezing and thawing de-creases compaction in soils subjected to coldweather. Taproots are effective in breakingdown compacted layers deep in the soil profilewhile shallow, fibrous roots break up compactedlayers near the soil surface (37). Active popula-tions of soil organisms also reduce soil compac-tion by forming soil aggregates and burrowinginto the soil.

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NUTRIENT RELEASE FROM

ORGANIC MATTER DECOMPOSITION

Manure and plant residues must be decom-posed by soil organ-isms before nutrients inthese materials areavailable for plant up-take. Soil organisms in-volved in nutrient de-composition require abalance of nutrients tobreak down organicmatter efficiently. Ma-nure and wasted for-ages are succulent ma-

None 10 tons 20 tons 30 tons

Organic Matter (%) 4.3 4.8 5.2 5.5

CEC (me/100g) 15.8 17.0 17.8 18.9

PH 6.0 6.2 6.3 6.4

Phosphorus (ppm) 6.0 7.0 14.0 17.0

Potassium (ppm) 121.0 159.0 191.0 232.0

Total pore space (%) 44.0 45.0 47.0 50.0

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From Magdoff and van Es, 2000 (Reference #1)

Manure application rate (tons/acre/year)

Time required for organicmatter decomposition isaffected by:• the carbon to nitrogen

ratio of organic matter• temperature• moisture• pH• diversity of soil organ-

isms


terials that have high nitrogen content and a goodbalance of nutrients for rapid decomposition.

Dried grasses, such as forages that died backover winter or during a drought, or manuremixed with wood bedding, have lower nitrogencontents and require more time for decomposi-tion. In addition, soil organisms may need toextract nitrogen and other nutrients from the soilto balance their diet and obtain nutrients notavailable in the organic matter they are decom-posing. Composting these materials increases theavailability of nutrients and decreases the poten-tial for nutrient immobilization when materialsare added to the soil. Tem-perature, moisture, pH,and diversity of soil organ-isms affect how rapidly or-ganic matter is decom-posed in the soil.

Nutrient release fromorganic matter is slow inthe spring when soils arecold and soil organismsare relatively inactive.Many farmers apply phos-phorus as a starter fertil-izer in the spring to stimulate seedling growth.Even though soil tests may indicate there is suf-ficient phosphorus in the soil, it may not bereadily available from organic matter during coolsprings.

NUTRIENT HOLDING CAPACITY OF

ORGANIC MATTER

Besides being a source of nutrients, soil or-ganic matter is critical for holding nutrientsagainst leaching or nutrient runoff. Stabilizedorganic matter or humus chemically holds posi-tively-charged plant nutrients (cations). Theability of soil particles to hold these plant nutri-ents is called cation exchance capacity or CEC. Con-tinual application of organic materials to soils in-creases soil humus (38) and enhances nutrientavailability, nutrient holding capacity, and soilpore space.

SOIL AGGREGATES

Soil humus is most effective in holding wa-ter and nutrients when it is associated with min-eral soil particles in the form of soil aggregates.

Soil aggregates aresmall, soft, water-stable clumps of soilheld together by fineplant-root hairs, fun-gal threads, humus,and microbial gels.Aggregates are alsoformed through theactivities of earth-worms. Research has shown that several spe-cies of North American earthworms annuallyconsume 4 to 10% of the soil and 10% of the total

organic matter in the top 7 inches of soil(39). This simultaneous consumption oforganic and mineral matter by earth-worms results in casts composed of as-sociations of these two materials. Earth-worms, as well as dung beetles, incor-porate organic matter into the soil as theyburrow.

Besides enhancing the nutrient andwater holding capacity, well-aggregatedsoils facilitate water infiltration, guardagainst runoff and erosion, protectagainst drought conditions, and are bet-

ter able to withstand compaction than less ag-gregated soils. Since aggregated soils are moregranular and less compacted, plant roots growmore freely in them, and air, water, and dissolvedplant nutrients are better able to flow throughthem. These factors increase plant access to soilnutrients.

To enhance aggregation within pasture soils,maintain an optimum amount of forages andresidues across paddocks, avoid the formationof bare areas, and minimize soil disturbance.Grazing can degrade soil aggregates by encour-aging mineralization of the organic glues that

hold aggregates to-gether. In areaswith a good coverof plant residues,animal movementacross pastures canenhance aggregateformation by incor-porating standingdead plant materi-als into the soil (40).


Soil mineralogy, long-term climatic condi-tions, and land-management practices affect soilpH. The acidity or alkalinity of soils affects nu-trient availability, nitrogen fixation by legumes,organic matter decomposition by soil organisms,and plant root function. Most plant nutrients aremost available for uptake at soil pH of 5.5 to 6.5.Legume persistence in pastures is enhanced bysoil pH of 6.5 to 7.0. In low-pH or acid soils, alu-minum is toxic to root growth; aluminum andiron bind phosphorus; and calcium is in a formwith low solubility. In high-pH or alkaline soils,calcium carbonate binds phosphorus while iron,manganese, and boron become insoluble.

Application of some synthetic nitrogen fer-tilizers acidifies soils. Soil microorganisms in-volved in nitrification rapidly transform urea orammonia into nitrate. This nitrification processreleases hydrogen ions into the soil solution,causing acidification, which decreases nutrientavailability, thus slowing the growth of plantsand soil organisms. Nitrificationalso occurs in urine patches whensoil microorganisms transformurea into nitrate.

Another fertilizer that acidifiesthe soil is superphosphate. Super-phosphate forms a highly acid (pH1.5) solution when mixed with wa-ter. The impact of this acidificationis temporary and only near wherethe fertilizer was applied, but, inthis limited area, the highly acid so-lution can kill rhizobia and other soil microor-ganisms (9).

The type and diversity of forage species inpastures can alter soil pH. Rangeland plants suchas saltbush maintain a neutral soil pH. Grassesand non-legume broadleaf plants tend to increasepH, while legumes tend to decrease it. The im-pact of plant species on pH depends on the typeand amounts of nutrients they absorb. Range-land plants absorb equal amounts of cation (cal-cium, potassium, magnesium) and anion (nitrate)nutrients from the soil. Grasses and non-legumebroadleaf plants absorb more anions than cationssince they use nitrate as their primary source of

nitrogen. Legumes that actively fix nitrogen usevery little nitrate; consequently, they reduce soilpH by taking more cations than anions (9). Acombination of legumes and non-legumes willtend to stabilize soil pH.

Pasture soils should be tested regularly to de-termine soil nutrients, soil organic matter, andpH. Based on test results and forage nutrient re-quirements, management practices can adjustsoil pH. Lime and organic matter increase soilpH and decrease soil acidity. Soil organic mat-ter absorbs positive charges, including hydrogenions that cause soil acidity (41). Lime increasessoil pH by displacing acid-forming hydrogen andaluminum bound to the edges of soil particlesand replacing them with calcium or magnesium.Limestone that is finely ground is most effectivein altering soil pH since it has more surface areato bind to soil particles. All commercial lime-stone has label requirements that specify its ca-pacity to neutralize soil pH and its reactivity,based on the coarseness or fineness of grind.

“Lime” refers to two types of materials, cal-cium carbonate and dolomite. Dolomite is a com-bination of calcium and magnesium carbonate.

Calcium carbonate is recommendedfor soils low in calcium; where grasstetany or magnesium deficiency isan animal health problem, dolomitelimestone should be used. In sandysoils or soils with low to moderatelevels of potassium, the calcium ormagnesium in lime can displace po-tassium from the edges of soil par-ticles, reducing its availability.Therefore, these soils should receiveboth lime and potassium inputs to

prevent nutrient imbalances.The timing of nutrient additions to fields or

pastures determines how effectively plants takeup and use nutrients while they are growing and

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Lime soils with cal-cium carbonate if thesoil is low in calcium.Use dolomite lime-stone if grass tetanyor magnesium defi-ciency is an animalhealth problem.

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setting seed. Different nutrients are importantduring different stages of plant development. Ni-trogen applied to grasses before they begin flow-ering stimulates tillering, while nitrogen appliedduring or after flowering stimulates stem and leafgrowth (9). However, fall nitrogen applications


for cool-season grasses are more effective andeconomical than spring applications. In mostyears, nutrient releases through mineralizationare sufficient to stimulate forage growth in thespring. Applications of nitrogen in the late sum-mer and fall allow cool-season grasses to growand accumulate nutrients until a killing frost.This provides stockpiled growth for winter graz-ing (42).

Both potassium and phosphorus are impor-tant for increasing the nutrient quality of forages,extending stand life, and enhancing the persis-tence of desirable species in the forage stand (42).Phosphorus is critical for early root growth, forseed production, and for effective nitrogen fixa-tion by legume nodules. Potassium is importantduring the mid-to-late growing season. It in-creases the ability of plants to survive winter con-ditions, by stimulating root growth and reduc-ing water loss through stomata or leaf pores (43).It also is important for legume vigor and for en-hancing plant disease resistance (42).

Nutrient uptake by plants corresponds totheir growth cycle. Warm-season forages exhibitmaximum growth during the summer, whereascool-season forages exhibit maximum growthduring the spring and early fall (32). Pasturescontaining a diverse combination of forages willuse nutrients more evenly across the growingseason while less-diverse pastures will showspikes in nutrient uptake requirements.

Legumes provide nitrogen to the pasture sys-tem through their relationship with the nitrogen-fixing bacteria, rhizobia. If nitrogen levels in the

soil are low, newlyplanted legumesrequire nitrogenfertilization untilrhizobia have de-veloped nodulesand are able to fixnitrogen. Oncethey start fixing ni-trogen, nitrogenfertilization de-

presses fixation by legumes since they requireless energy to take up nitrogen from the soil thanthey need to fix nitrogen. Legumes can fix up to200 pounds of nitrogen per year, most of whichbecomes available to forage grasses in the fol-lowing years. Phosphorus is essential for effec-

tive nodule formation and nitrogen fixation. Inacid soils, liming may make phosphorus alreadyin the soil more available, thereby decreasing theneed for fertilization.

As discussed above, the type of organic ma-terial added to the soil, as well as temperature,moisture, pH, and diversity of soil organisms,determines how rapidly soil organisms decom-pose and release nutrients from organic matter.Synthetic fertilizers are soluble and immediatelyavailable for plant uptake. Therefore, these fer-tilizers should be applied during periods whenplants can actually use nutrients for growth. Alag time of two to 21 days may pass after fertiliz-ers are applied before increased forage produc-tion is observed.

Organic material releases nutrients over aperiod of several years. On average, only 25 to35% of the nitrogen inmanure is mineral-ized and availablefor plant use duringthe year of applica-tion. Another 12%is available in thefollowing year, 5%in the second yearfollowing application, and 2% in the third year(44). Manure deposited in pastures causes an in-crease in forage growth approximately 2 to 3months after deposition, with positive effects ongrowth extending for up to two years (11). Al-falfa can supply approximately 120 pounds ofnitrogen to crops and forages in the year after itis grown, 80 pounds of nitrogen during the fol-lowing year, and 10 to 20 pounds in the thirdyear (44). Because of this gradual release of nu-trients from organic materials, continual addi-tions of manure or legumes will compound theavailability of nutrients over time. Accountingfor nutrients available from previous years iscritical for developing appropriate applicationsrates for manure and fertilizers during eachgrowing season. Not accounting for these nutri-ents can result in unnecessary fertilizer expensesand risks of nutrient losses to the environment.

Nutrients from both organic and syntheticfertilizers can be lost through leaching, runoff,or erosion. The potential for nutrient losses isgreatest if these materials are applied in the fallor winter, when plants are not actively growing

Nitrogen fertilizationdepresses fixation bylegumes since they re-quire less energy totake up nitrogen fromthe soil than they needto fix nitrogen.

A lag time of two to 21days may pass afterfertilizers are appliedbefore increased for-age production is ob-served.


Ensure plant cover and diversity across pastures

• Use management practices that maintain a complete cover of forages and residuesacross pastures

• Combine bunch-grass species with a diversity of forage species, including plantswith prostrate growth habit, to provide both good water infiltration and protectionagainst erosion and soil compaction

Grazing management practices during wet weather

• Use well-drained pastures or a “sacrificial pasture” that is far from waterways orwater bodies

• Avoid driving machinery on pastures that are wet or saturated

• Avoid spreading manure or applying fertilizers on soil that is saturated, snow-cov-ered, or frozen

Ensure effective use of nutrient inputs

• Use management practices that encourage the even distribution of manure and urineacross paddocks

• Rely on soil tests and other nutrient management practices when applying fertilizersand manure to pastures

• Account for nutrients available form manure and legume applications during prioryears when developing fertilizer or manure application rates for the current year

• Sample the nutrient content of added manure to determine appropriate rates of ap-plication

• Choose the appropriate type of limestone to apply for pH adjustment based on cal-cium and magnesium needs and balances in pastures

• Either avoid the use of fertilizers that decrease soil pH or use lime to neutralize soilsacidified by these fertilizers

• Apply nitrogen fertilizer in the fall to enhance the amount of forages stockpiled forwinter grazing

• Apply sufficient phosphorus and potassium while limiting additions of nitrogen in or-der to favor growth of legumes in your pastures

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or during times when soils are frozen, snow-covered, or saturated. During times of high rainfall,nitrate may leach through the soil since it does not bind to soil particles. Rainfall also facilitates thetransport of phosphorus to water bodies in runoff water or through artificial drainage tiles. Rainfallor snowmelt water flowing over bare soil causes soil erosion and the transport of nutrients attachedto soil particles.


Farmers and ranchers graze animals using avariety of management methods. In this docu-ment, extensive grazing refers to the practice ofgrazing animals continuously or for extendedperiods of time on a large land area. Rotationalgrazing is a management-intensive system thatconcentrates animals within a relatively smallarea (a paddock) for a short period of time —often less than a day for dairy animals. The ani-mals are then moved to another paddock, whilethe first paddock is allowed to recover and re-grow. Animals are moved according to a flex-ible schedule based on the herd size, the amountof land available, quality of forages in the pad-dock, and forage consumption. Grazing manag-ers determine when and how long to graze ani-mals in specific paddocks based on climatic con-ditions, soil characteristics, land topography, andthe distance the paddock is from streams or riv-ers.

Pasture size, shape, and topography; stock-ing rate; grazing duration; and time of day allaffect how animals graze, lounge, drink water,and use feed or mineral supplements. Also, dif-ferent animal species vary in their use of nutri-ents and their herding behavior. These factors,along with soil characteristics, climate, and for-age and soil management practices, affect nutri-ent cycling in pastures, animal growth and pro-ductivity, and potential of manure nutrients tocontaminate ground or surface water.

Grazing animals that receive no mineral orfeed supplements will recycle between 75 and85% of forage nutrients consumed. If no fertil-izer or outside manure inputs are applied, con-tinual grazing will cause a gradual depletion ofplant nutrients. Animals provided feed or min-eral supplements also deposit 75 to 85% of thenutrients from these inputs as urine and feces(42). These nutrients represent an input into thepasture system. Nutrient inputs from non-for-age feeds can be substantial for dairy and otheranimal operations that use a high concentrationof grain and protein supplements, importing intothe pasture approximately 148 lbs. N, 32 lbs. P,and 23 lbs. K per cow per year (42). Winter feedsalso form a substantial input into the pasture nu-trient budget when animals are fed hay while be-ing kept on pasture.

MANURE DEPOSITION AND

DISTRIBUTION

A cow typically has 10 defecations per day,with each manure pile covering an area of ap-proximately one square foot (47). They will alsourinate between eight and 12 times per day (48).Each urination spot produces a nitrogen appli-cation equivalent to 500 to 1,000 lbs./acre whileeach defecation represents a nitrogen applicationrate of 200 to 700 lbs./acre (42). An even distri-bution of nutrients throughout a paddock is re-quired for productive plant and animal growth.

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NUTRIENT BALANCES

Maintaining a balance between nutrients re-moved from pastures and nutrients returned topastures is critical to ensure healthy and produc-tive forage growth, as well as to control nutrientrunoff and water-body contamination. Nutrientbalances in pastures are determined by subtract-ing nutrient removals in the form of hay harvested,feed consumed, and animals sold, from nutrientinputs including feed, fertilizer, and manure.

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From Klausner, 1995 (Reference #44)

Farm Boundary OutputsInputs

feed

animalproducts

crops

fertilizer

legume N

rainfall

Losses

ammonia volatilization, leaching,denitrification, runoff, & erosion


Unfortunately, grazing animals do not naturallydeposit urine and feces evenly across the paddockswhere they graze. In one rotational grazingstudy, urine spots occupied 16.7% of the pasture,while manure spots occupied 18.8%, following504 grazing days per acre (49). Intensity of graz-ing rotations affects the distribution of manurecoverage in paddocks. Under continuous, exten-sive grazing practices, 27 years would be neededto obtain one manure pile on every square yardwithin a paddock; if a two-day rotation were usedinstead only two years would be needed (42).

Nutrient concentration within pastures re-sults from the tendency of grazing animals to con-gregate. They tend to leave manure piles or urinespots around food and water sources, on sidehills, in depressions, along fence lines, and un-der shade. Sheep have a greater tendency thancattle to congregate and deposit manure in theseareas (50). Prevailing wind direction and expo-sure to sunlight can also affect animal movement,congregation, and manure deposition (51).Laneways that connect pastures or lead to wa-tering areas are another area of animal congre-gation and manure deposition. When animalshave to walk more than 400 feet from the pas-

ture to water, they deposit between 13 and 22%of their manure on laneways (47, 52).

A study conducted in Iowa showed a buildupof nutrients extending 30 to 60 feet into the pas-ture around water, shade, mineral supplements,and other areas where cattle congregated (53).Nutrients are concentrated in these congregationareas because animals transport nutrients fromareas where they graze. Consequently, they alsodeplete nutrients from the grazing areas. Graz-ing practices that encourage foraging and manuredistribution across paddocks and discourage con-gregation in limited areas will improve nutrientbalances within pastures.

The time of day when animals congregate indifferent areas determines the amount and typeof nutrients that accumulate in each area. Ani-mals tend to deposit feces in areas where theyrest at night or ruminate during the day, whilethey urinate more in the areas where they grazeduring the day (47). Nitrogen is present in bothfeces and urine while phosphorus is primarilydeposited as feces, and potassium is foundmostly in urine. While most urine is depositedduring the day, urine that is deposited at nighthas a higher nutrient content than urine depos-ited while grazing (41). As a result of these fac-

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Dairy cows Beef /SheepFeed consumption/day 18–33 lbs.Nutrients used for growth and reproduction 17% N 15 -25% N

26% P 20% P, 15% K

Nutrients removed from pasture in form N 84 lbs./cow N 10 lbs./cow-calfof milk and meat P 15 lbs./cow P 3 lbs./cow-calf

K 23 lbs./cow K 1 lbs./cow-calf

Nutrients/ton manure 6–17 lbs.N3–12 lbs.P

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5

2-15 lbs. K2ONitrogen content of feces 2.0–3.6% 3.4–3.6%Nitrogen excreted as feces 55 lbs./yearNitrogen content of urine 0.42–2.16% 0.30–1.37%Nitrogen excreted as urine 165 lbs./year

From Stout, et al. ( 45), Detling ( 46), Russelle ( 17), Wells and Dougherty ( 47) ,Haynes and Williams ( 41), Klausner ( 44), Lory and Roberts ( 42)

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tors, phosphorus will accumulate in resting ar-eas (13) while nitrogen and potassium will accu-mulate in both resting and grazing areas.

MINIMIZING ANIMAL CONGREGATION

By working with the normal foraging andherding behavior of grazing animals, distribu-tion of animals across paddocks can be encour-aged. In larger paddocks, animals tend to grazeand lounge as a herd, while they distribute them-selves more evenly across smaller paddocks (41).In larger paddocks, animals visit water, miner-als, shade, and fly-control devices as a herd,whereas animals concentrated within small pad-docks tend to visit these areas one-by-one. Lo-cating nutrients, shade, and pest-control devicesfarther apart in the paddock further discouragesconcentration of animals and manure. If a par-ticular area of a paddock is deficient in nutrients,placement of supplemental feeds in that area canbe used to encourage congregation and manuredeposition there.

Subdividing depressions, side hills, andshady areas among several paddocks can en-hance nutrient distribution across the landscape.Research conducted in Missouri showed thatmanure nutrients were distributed more evenlyacross the landscape when a field was managedusing 12 or 24 paddocks rather than only threepaddocks (54). Animals in the smaller paddocksconcentrated around favored areas for less timethan did animals in larger paddocks. Since ani-mals tend to graze along the perimeter of fencelines, they distribute nutrients most evenly acrosspaddocks that are small, square, and have wateravailable (55). An efficiently designed paddockallows animals to graze and drink with a mini-mum amount of time, effort, and trampling ofthe pasture sod.

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Manure deposition as affected by paddock size (fromPeterson and Gerrish, Reference 52).

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While feces contain nitrogen predominantlyin the organic form, 60 to 70% of cow-urine ni-trogen and 70 to 80% of sheep-urine nitrogen isin the form of urea. Urea and potassium in urineare soluble and therefore immediately availablefor plant uptake. Phosphorus in feces is predomi-nantly in the organic form and must undergo de-composition before it is available to plants. Soil

O = water tank

O = water tank

O = water tank


organisms will decompose moist, nitrogen-richmanure piles derived from succulent grasses rela-tively quickly. They will have difficulty break-ing down manure derived from hay or older for-ages that is stiff, dry, and crusty. When a hardcrust forms on manure piles during dry weather,both physical breakdown and biological decom-position are inhibited (41). By treading on ma-nure piles as they move around a pasture, ani-mals physically break these piles into smallerpieces that are more easily consumed by soil or-ganisms.

Because nutrients are released slowly frommanure, forage plants in the vicinity of manurepiles will grow slowly for about two months fol-lowing manure deposition (41, 42). However, asdecomposition of manure piles by soil organismsmakes nutrients available for plant use, greaterpasture regrowth and forage production occursin the vicinity of manure and urine compared toother pasture areas (49, 54, 56). Increases in ni-trogen availability in areas near manure piles canfavor the growth of grasses compared to legumes(9), an impact that can last for up to two years(41).

Animals naturally avoid grazing near dungsites, but will feed closer to manure piles (41) anduse forages more efficiently as grazing pressureintensifies. In multispecies grazing systems,sheep do not avoid cattle manure as much ascattle do (57). While both sheep and cattle avoidsheep manure, the pellet form of sheep manurehas a large surface area, and thus breaks downmore rapidly than cattle manure. Consequently,forages are used more effectively when cattle arecombined with sheep.

haying. Prior to the current concerns over waterquality, manure application recommendationswere made to meet forage needs for nitrogen.Continued nitrogen-based applications result ina phosphorus build-up in the soil since manureusually contains about the same concentrationof phosphorus and nitrogen, while plants onlyrequire one-half as much phosphorus as nitro-gen. In diverse pastures that contain a combina-tion of grasses and legumes, decreasing or elimi-nating manure applications can lower phospho-rus imbalances while maintaining forage yields.Nitrogen fixation by legumes helps satisfy for-age nitrogen requirements while using excess soilphosphorus.

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Manure and fertilizers are applied to pasturesto provide nutrients necessary to obtain effective

plant growth andanimal production.Applications shouldbe based on regularsoil testing, the abil-ity of soil to provideand retain nutrients,plant needs, grazingintensity, and nutri-ent removals through

Fertilizer and manureapplications shouldbe based on regularsoil testing, the abil-ity of soil to provideand retain nutrients,plant needs, andgrazing intensity.

On some farms, manure is applied to soil asa waste product. Instead of being applied ac-cording to crop needs, manure is primarily ap-plied according to the need to dispose of manure,the location of fields in relation to the barn, andthe accessibility of fields during bad weather.These “waste application” practices present ahigh potential for nutrient buildup and move-ment of excess nutrients to ground or surfacewaters.

To ensure that manure is used effectively asa source of plant nutrients and poses minimalrisks to the environment, it should be appliedaccording to a nutrient management plan. Natu-ral Resources Conservation Service or Soil andWater Conservation District personnel, as well

Applying manure to meet the nitrogen needsof corn (about 200 lbs. N/acre) adds muchmore phosphorus than corn needs.

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as many commercial crop consultants, are trained in the development of nutrient management plans.Software programs to develop your own nutrient management plan may be available from Coopera-tive Extension Service educators or Agronomy and Soil Science specialists at land grant universities.

cies, enhances the dispersal of forage seeds, andhelps conserve nutrient resources within the soil-plant system.

GRAZING BEHAVIOR, PLANT GROWING

POINTS, AND PLANT LEAF AREA

Grazing habits of different animal specieshave different impacts on forage species compo-sition in pastures. For example, horses graze

more closely to the groundthan cattle; sheep graze atsoil level and can take awaythe base of grass plants be-low the area of tiller emer-gence (59); while cattle tendto graze taller grasses thatsheep may reject. Animalgrazing behavior, the loca-tion of a plant’s growingpoint, and the amount of

leaf area remaining when animals are rotated toanother pasture affect the ability of plants to re-grow. If grazing animals remove the growingpoint and substantial leaf area of grasses, newleaf growth must come from buds that have beendormant and the energy for this growth must

DEFINITION

Grazing intensity refers to the impact animalshave on forage growth and reproduction and onsoil and water quality. It is influenced by ani-mal foraging habits, stock-ing rates, the length of timeanimals are allowed tograze within a given pad-dock, and the relation thesefactors have to soil charac-teristics and climatic condi-tions. Continuous high-in-tensity grazing depletes soilnutrients, decreases the di-versity of forage species, in-hibits the ability of some forage plants to regrowand reproduce, and increases the potential fornutrient runoff and erosion. Conversely, short-term high-intensity grazing combined with aresting period (as in rotational grazing practices)causes an increase in the diversity of forage spe-

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Components of a Comprehensive Nutrient Management Plan• Soil tests on all fields or paddocks• Manure tests• Load-capacity and rate-of-application of manure spreading equipment• Timing and method of manure and fertilizer applications• Prior land management practices including manure applications, legumes used as green

manures, fallows, or hay removal• Assessments of runoff, erosion, and flooding potentials for each field or paddock• Crops or forages to be produced• Current pasture management practices, including stocking rates and hay removal

Format of a nutrient management plan for each paddock or field• Soil and manure test results• Risk factors such as excess nutrient levels, or high runoff, erosion, or flooding potential• Recommended time, method, and rate for fertilizer and manure applications• Recommended time for grazing, especially on pastures with moderate to high potentials for

runoff, erosion, or flooding• Management practices to minimize risk factors and maximize nutrient availability to forages

Short-term high-intensity grazingcombined with a resting period (asin rotational grazing practices)causes an increase in the diversityof forage species, enhances the dis-persal of forage seeds, and helpsconserve nutrient resources withinthe soil-plant system.

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come from stored carbohydrates rather than fromphotosynthesis (60).

Early in the growing season, all grasses havetheir growing points at or near ground level.Ryegrass, tall fescue, Kentucky bluegrass andmany other species of cool-season grasses havegrowing points that remain at or below groundlevel throughout most of the growing season.Other, predominantly native, grass species — in-cluding smooth broomgrass, timothy, reedcanarygrass, switchgrass, and gamagrass — havestems that elongate below the growing pointabove the soil level (60). As long as the growingpoint remains intact, the plant is capable of pro-ducing new leaves. Grasses with low growingpoints are able to recover from grazing relativelyquickly because the growing point is not dis-turbed. If the growing point is removed, growthrecommences from the emergence of new tillers.Under continuous, intensive grazing practices,warm-season grasses recover more slowly thancool-season grasses, especially during the spring(61). As a result, continuous grazing practices orgrazing too early in the season tends to favor thegrowth of non-native grasses and decrease thediversity of forages in pastures (62).

include treading impact on leaf and root growth,forage composition impact on the ability of plantsto intercept sunlight for photosynthesis, and soilconditions (35).

NUTRIENT UPTAKE

Forage plants that are cut or regrazed fre-quently during the growing season take up morenutrients than forages that are not cut or grazed.Research conducted in Kansas indicated thatcutting pasture forage six times during the grow-ing season resulted in 4.3 times greater nitrogencontent and 5.2 times greater phosphorus con-tent in cut forages compared to uncut plots (63).Cutting pastures in the spring when seed headsare forming can also increase the productivityand nutrient uptake of pasture forages (64).Other studies (56, 65) demonstrated that in-creased grazing intensity resulted in younger,more succulent plants with a higher nitrogencontent compared to plants growing in ungrazedareas. The higher nitrogen content was attrib-uted to return of nitrogen to the system throughurine and to the availability of nitrogen fixed bylegumes. In these studies legumes remainedprevalent in the more intensely grazed plotswhile their populations decreased in the morelightly grazed paddocks (65).

YIELD

During the first year of intensive grazing,increasing the intensity of cutting or grazing in-creases the amount of forage produced. Follow-ing grazing, photosynthesis is stimulated andplants take up more nutrients. This permits leafregrowth in broadleaf plants and increasedtillering in grasses. Increased leaf area then al-lows for greater photosynthesis. As photosyn-thesis and the formation of carbohydrates in-crease, nutrient uptake by roots and subsequentmovement of nutrients from roots to leaves alsoincrease. However, as more energy and nutri-ents are allocated to leaf production and in-creased photosynthesis, less energy and nutri-ents are provided for root growth (63).

Continuous grazing tends to favor thegrowth of cool- season grasses since graz-ing animals remove the elevated growingpoints of native warm-season grassesmore readily than they remove the lowergrowing points of non-native, cool-seasongrasses.

For areas with moderate rainfall, leaf arearemaining after grazing is more critical for for-age recovery than the location of a forage plant’sgrowing point (J. Gerrish, personnal communi-cation). Most forbs and legumes, such as alfalfaand red clover, have aerial growing points rela-tively high up on the plant, which are easily re-moved by grazing animals. This is not detrimen-tal to plant growth unless a majority of the leafarea or the basal portion of the plant is removed.For optimal recovery, at least 3 to 4 inches of re-sidual leaf area should remain on cool-seasongrasses while 4 to 8 inches of leaf area shouldremain for warm-season grasses following graz-ing (61). Other factors that affect plant regrowth

Frequently grazed plots exhibit high bio-mass production and nutrient uptake dur-ing the initial grazing season. But if graz-ing intensity is too great, forage produc-tion will decrease in the following years.


While frequently mowed or grazed plots ex-hibit high biomass production and nutrient up-take during the initial grazing season, if the in-tensity of grazing is too high, forage productionwill decrease in following years (63, 66). Thisproduction decline results from decreased plantability to take up nutrients because of decreasedroot growth and depletion of soil nutrients. Se-vere grazing will also impact plant diversity,since grazing during flowering removes seedheads and flowers, limiting the reseeding of for-age plants (64).

(65). Grazing or cutting pastures too short canalso expose bare soil to the impact of rainfall, in-creasing the potential for soil compaction and theloss of topsoil and nutrients through erosion.Nutrient cycling and effective nutrient use byplants depend on pasture management practicesthat minimize soil compaction, conserve organicmatter, and do not hinder plant regrowth follow-ing grazing.

Diverse forage mixtures of both broadleavedplants and grasses use solar energy efficiently.The shape and orientation of plant leaves affecthow and when the plant can best conduct pho-tosynthesis. Tall plants and upright grasses cap-

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A sufficient resting period allowsplants to regrow and produce ad-equate leaf area for photosynthe-sis. It also allows plants and soilorganisms to reduce soil compac-tion and increase the availability ofnutrients through mineralization.

Root growth is critical for water and nutrientuptake. Plants can also store food reserves inroots to allow for regrowth during periods ofstress. Plants grazed too frequently or cut tooshort have difficulty producing more leaves be-cause of limited growth and food reserve stor-age by roots. In one study, plants that were notcut until they reached eight inches tall producedmore growth than plants cut every time theyreached two inches tall. Similarly, grasses sub-jected to continuous intensive grazing by sheepproduced less vegetation than lightly grazed pas-tures. In both cases, a longer resting period re-sulted in better plant growth, since the restingperiod allowed plants to regrow and produceadequate leaf area for photosynthesis (63). Grasstiller population and pasture production mark-edly increased in an extensively grazed pasturethat was fallowed for one year. This resting pe-riod allowed plants and soil organisms to reducesoil compaction and increase the availability ofnutrients through mineralization (67).

Cutting grasses short not only depressesplant regrowth, it also increases soil temperature.As soil temperature increases so does nutrientmineralization by soil organisms. While miner-alization is necessary to release nutrients fromplant and animal residues, if mineralization istoo rapid, it can cause a loss of organic matter

Nutrient cycling and effective nutri-ent use by plants depend on pas-ture management practices thatminimize soil compaction, conserveorganic matter, and do not hinderplant regrowth following grazing.

The nutrient content of forage plants affectsanimal feeding habits, the amount of nutritionanimals obtain, and the type of manure they pro-duce. Succulent, nutritionally balanced pasturesprovide good animal productivity and cause ani-mals to deposit moist manure piles (36). Ani-mals feeding on dry, older, or overgrazed for-ages will obtain limited nutrient value. Manurepiles produced from these forages will be stiffbecause of their high fiber content. Dry, stiffmanure piles are difficult for soil organisms todecompose since there is little air within the pile(68). Conversely, animals often deposit very liq-uid manureasthey begin feeding on pastures inthe spring after a winter of eating hay. The highmoisture content of the pasture forages resultsin a very wet manure pile that disperses acrossthe soil. Soil organisms are able to decomposemanure that has relatively high nitrogen andmoisture content more readily than manure thatis drier and more carbon-rich.


White clover has rhizomes rather than a tap-root. This growth habit allows it to colonize bare

soils (64) by form-ing additionalplants through thegrowth of stolons.White clover iscompetitive withgrass at low pro-duction densitieswhile legumeswith taproots aremore competitiveat high productiondensities (70).

The diversityof forage speciesalso affects thepersistence of le-gumes within apasture. When sixto eight forage spe-cies were planted

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Root growth of alfalfa un-der irrigated (left) and dry(right) conditions (Weaver,Reference 71).

Timing of grazingaffects speciescomposition anddiversity in pas-tures.

Nitrogen transfer between grasses and le-gumes is greatest when there is a closepopulation balance between these speciesand they are growing close together.

together in a Missouripasture, pasture plantdiversity remained highafter three years of graz-ing. Pastures with a di-versity of forage speciesalso maintained a higher

percentage of forage cover during this time thanpastures planted to monocultures or simple mix-tures of forages (72). Productivity within pas-tures is more stable when forages provide a di-versity of function and structure, such as height,root growth habit, life cycle, and habitat require-ments (4).

ture light at the extreme angles of sunrise andsunset while horizontal leaves of broadleaf plantsuse sunlight better at midday. A combination oftall sun-loving plants with shorter shade-toler-ant plants allow for the capture of both directand filtered sunlight. A combination of warm-and cool-season grasses allows for effective pho-tosynthesis throughout the growing season.Warm-season grasses like big bluestem are bet-ter able to grow and use solar energy at tempera-tures between 90 and 100°F, while cool-seasongrasses like tall fescue grow best between 75 and90°F (32).

PERSISTENCE OF PASTURE LEGUMES

Maintaining legumes as part of the foragemix is necessary if nitrogen fixation is to providemost of the nitrogen input to the pasture system.Legumes with a deep taproot and a woodycrown, such as alfalfa, red clover, and birdsfoottrefoil, are able to persist in a well-drained pas-ture because they are able to obtain water andnutrients from deep below the soil surface. Theyalso tolerate drought and cold, and are able toregrow unless their growing points are elevatedand exposed to defoliation. Rotational grazinghas been shown to increase the proportion of redclover and alfalfa in mixed pastures (69).

Nitrogen fixation is directly related to the abil-ity of legumes to accumulate energy through pho-tosynthesis. Thus, leaf removal decreases nitro-gen fixation, and leaf regrowth increases the po-tential for nitrogen fixation. Legumes not onlyfix nitrogen for their own needs, but are also ableto supply nitrogen to non-nitrogen-fixing foragecrops. They primarily supply nitrogen to forageplants following decomposition. Pastures domi-nated by clover produce around 200 pounds ni-trogen per acre per year through nitrogen fixa-tion.

Legumes can also provide nitrogen to com-panion grass species during the growing season.In New Zealand, perennial ryegrass obtained 6to 12% of its nitrogen from associated white clo-ver. Alfalfa and birdsfoot trefoil provided up to75% of the nitrogen used by reed canarygrass inMinnesota. This nitrogen transfer occurs whenroots die, nodules detach, or neighboring grassesand legumes become interconnected by their rootsor through mycorrhizae. Nitrogen transfer be-tween grasses and legumes is greatest whenthere is a close population balance between thesespecies and they are growing close together (15).In the first year of legume establishment, nitrogentransfer is relatively low and is derived predomi-nantly from nodule decomposition; it increases inthe second year as direct-transfer mechanismsthrough mycorrhizae become established (14).


NUTRIENT USE EFFICIENCY

A diverse plant community uses soil nutri-ents more effectively than a monoculture orsimple plant mixtures. Native grasses have alower requirement for nitrogen and subsequentlya lower concentration of nitrogen in their leaf tis-sue compared to non-native cool-season grasses.As a result, these grasses thrive under low nutri-ent conditions but they provide lower-qualityfeed and recycle nutrients more slowly back tothe soil system. The low nitrogen content of theplant litter results in slow decomposition, immo-bilization of nitrogen by organisms involved indecomposition, and a decrease in the nitrogenavailable for plant uptake.

Just as a diverse plant canopy covers theentire soil surface, a diversity of root sys-tems occupies the entire soil profile.

(73). Due to their high nitrogen content, decom-position of residues from these plants stimulatesthe mineralization or release of nutrients into thesoil solution. Cool-season and warm-season for-ages grow and take up nutrients at different timesof the year. A combination of cool- and warm-season forages ensures a relatively even uptakeof nutrients throughout the growing season.

Just as a diverse plant canopy covers the en-tire soil surface, a diversity of root systems occu-pies the entire soil profile, from the soil surfacedown as far as 15 feet. Grasses generally havefine bushy roots. Legumes such as alfalfa or redclover have taproots. Some plants have longeror deeper root systems while other plants have aroot system that grows primarily in the surfacesoil. Pastures that contain plants with a diver-sity of root systems will be better able to harvestand use nutrients from the soil than a less di-verse community. Plants with more shallowroots are effective in recycling nutrients releasedthrough the decomposition of thatch and manureon the soil surface, while deep-rooted plants areable to scavenge nutrients that have been leacheddown through the soil profile.

Manure is unevenly distributed,concentrated near the fenceline

Broadleaf plants require higher nitrogen in-puts for productive growth and have higher ni-trogen content in their plant tissues than grasses


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Balance nutrient inputs and outputs• Replenish nutrients removed by grazing animals• Recognize that feed supplements, particularly for dairy cows, represent significant nutri-

ent inputs onto farms• Replace nutrients based on a comprehensive nutrient management plan that takes into

account prior manure additions, nitrogen contributions from legumes, and soil tests• Apply manure based on the phosphorus needs of forages in order to avoid phosphorus

build up on pastures; rely on legumes to supply much of the nitrogen needed for foragegrowth

Promote even distribution of manure nutrients across paddocks• Subdivide pastures to distribute congregation areas among several paddocks• Keep paddock dimensions as close to square as possible• Provide animals with water in every paddock; avoid use of laneways to access water• Locate nutrient supplements, shade, water, and pest-control devices far apart from one

another

Enhance nutrient availability• Enhance growth of soil organisms involved in the decomposition of manure by maintain-

ing good soil quality and minimizing use of soil-applied insecticides and high-salt fertiliz-ers

• A combination of cattle and sheep enhances the amount of land available for grazingsince sheep graze closer to cattle manure than cattle do and feed on coarser vegetationthan cattle will use

Encourage a diversity of forage species within paddocks• Maintain a diversity of forages representing a variety of leaf and root growth habits, life

cycles, and habitat preferences• Rotate pastures while at least 4 inches of the leaf area remains. This allows plants to

regrow rapidly and roots to recover• Maintain a high percentage of legumes in the forage mix by not overgrazing and by

minimizing nitrogen fertilizer additions• Provide paddocks with sufficient rest time to allow forages to regrow


Soil organisms play a critical role in nutrientcycling. Not only are they responsible for de-composing organic matter, forming soil aggre-

gates, solubilizing min-eral nutrients, and ad-justing soil pH; they arealso responsible for ni-trogen fixation, nitrifi-cation, phosphorus up-take through my-chorrizae, degradationof soil minerals, andformation of plant hor-mones. A healthy soilcontains millions of or-

ganisms, ranging from visible insects and earth-worms to microscopic bacteria and fungi. Anacre of living soil may contain 900 pounds ofearthworms, 2400 pounds of fungi, 1500 poundsof bacteria, 133 pounds of protozoa, and 890pounds of arthropods and algae, as well as smallmammals. The term soil food web refers to thenetwork of dynamic interactions among these or-ganisms as they decompose organic materialsand transform nutrients.

While some of the organisms in this diversecommunity are plant pests, many more serve asantagonists of plant pests and diseases. Othersoil organisms, particularly bacteria, are able touse toxic chemicals, such as pesticides, as a sourceof food. As they consume these toxic chemicals,they break them down into substances, such ascarbon dioxide, water, and atmospheric nitrogen,that are either non-toxic or less-toxic to plants,animals, and humans.

SOIL ORGANISMS

Many soil organisms are involved in the de-composition of organic matter. Larger soil or-ganisms, including small mammals, insects, andearthworms, are primary decomposers, involved inthe initial decomposition and cycling of nutri-

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Soil food webrefers to the net-work of dynamici n t e r a c t i o n samong these or-ganisms as theydecompose or-ganic materialsand transformnutrients.

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Springtails

Predatory mites

Predatory nematodes

Amoebas

Bacteria-feedingnematodes

Bacteria

FungiSoil organic

matter &residues

Mycorrhizae

Root-feedingnematodes

Roots Fungus-feedingmites

Fungus-feedingnematodes

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ents. Primary decomposers make greater use ofcarbon than of nitrogen in their growth and res-piration processes. As a result, the feces and castsdeposited by them have a lower carbon contentand a lower ratio of carbon to nitrogen than theoriginal organic matter. By transforming organicmatter into a simpler chemical form as well asphysically breaking it down into smaller pieces,primary decomposers make these materials moreavailable to microorganisms or secondary decom-


posers for further breakdown. Because the deadbodies of earthworms and insects are high in ni-trogen, they are easily decomposed by soil mi-croorganisms (75). Fungi and bacteria are pre-dominant secondary decomposers, but algae,protozoa, amoebas, actinomycetes, and nema-todes also play important roles in transformingsoil nutrients.

The chemistry of organicmaterials and environmentalconditions determines howrapidly organic matter is bro-ken down, which soil organ-isms are involved in the de-composition process, andwhether organic matter de-composition will cause an ini-tial decrease or increase inavailable nutrients. The soilenvironment determineswhich soil organisms aredominant and which soil or-ganisms are less active. Somebacterial species thrive under flooded, anaero-bic conditions but most soil organisms requireaccess to oxygen. Earthworms and some soil in-sects require soil that is aggregated and relativelyuncompacted so they can burrow through it.Environments with limited nitrogen availabilityare dominated by organisms that are able to fixnitrogen from the atmosphere, such as algae, li-chens, and rhizobia associated with legumes.Many soil organisms are killed by non-specificinsecticides as well as by highly concentrated fer-tilizers such as anhydrous ammonia.

As discussed previously, organic materialsthat are old or woody, such as tree branches, oldroots, or dried grass, contain a large amount ofcarbon compared to nitrogen. To decomposethese materials, soil organisms may need to ex-tract nitrogen from the soil solution in order tobalance their carbon-rich diet, thus temporarilyreducing the amount of nitrogen available forplant use. Young, succulent, “first-growth” plantmaterials, fresh manure, and materials that havegone through primary decomposition processesby larger soil organisms contain a higher con-centration of nitrogen in relation to carbon. Soilorganisms more readily decompose these mate-rials and make the nutrients in them availablefor plant uptake.

The type of organic matter will influence thetype of soil organisms involved in the decompo-sition process. As each decomposer feeds, it usessome nutrients for its own growth and reproduc-tion and releases other nutrients into the soil so-lution where they are available for plant growthand production. Decomposer organisms mayalso excrete organic materials that can either be

further broken down byother soil organisms orbecome part of the soilhumus.

In general, bacteriarequire more nitrogen inorder to break down or-ganic matter than domost fungi. Fungi arethe dominant decom-poser in forest environ-ments since they requireless nitrogen in their dietand are able to feed onwoody, older, or more

fibrous materials. They are also able to surviveand replicate in environments that are less moistthan those required by bacteria. Bacteria are moreprevalent in garden and pasture environmentsbecause they require higher amounts of nitrogenand moisture, and because they feed readily onfresh manure, young grasses, legumes, and othereasy-to-decompose materials (10).

The chemistry of organic materialsand environmental conditions deter-mines:• how rapidly organic matter is

broken down• which soil organisms are in-

volved in the decomposition pro-cess

• whether nutrient availability willincrease or decrease in the shortterm

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Earthworms are primary decomposers of leaflitter and manure piles. Research conducted inDenmark showed that earthworms were respon-sible for 50% of the breakdown and disappear-ance of cow manure, while dung beetle larvaeaccounted for between 14 and 20% (76). Theseorganisms also consume fresh organic materials,then deposit their feces in the soil. When theyburrow, they move manure and other organic

Earthworms and dung beetles are visibleindicators of soil health: their presenceshows that nutrient decomposition pro-cesses are occurring and the soil foodweb is effectively operating.


materials into the soil, where it is more acces-sible to other organisms involved in decomposi-tion. Burrowing organisms also aerate the soil.Good aeration promotes the growth of the ma-jority of organisms involved in organic matter de-composition. For this reason, earthworms anddung beetles are visible indicators of soil health:their presence shows that nutrient decomposi-tion processes are occurring and the soil food webis effectively operating.

EARTHWORMS

According to research studies, the weight ofearthworms in the soil is directly related to pas-ture productivity (77). In healthy soils with abun-dant earthworms, these or-ganisms consume between65 and 80 tons of manureper acre per year (39).Earthworms also breakdown pasture thatch andincorporate organic matterfrom the thatch into thesoil. Where few or no earthworms are present,pastures develop a thick thatch layer, slow ratesof organic matter decomposition, and a poorcrumb structure (39).

Decomposition of organicmatter by earthworms speedsup the breakdown and releaseof plant nutrients, particularlynitrogen and phosphorus.Earthworms consume low-ni-trogen plant materials as wellas high-nitrogen manure (39).Under pasture conditions,earthworms have been shownto mineralize 10 pounds peracre per year of phosphorusin their casts (5). Earthworms also facilitate thetransformation of straw and leaf litter into soilhumus (78). The earthworm gut combines de-composed organic matter with particles of min-eral soil and microorganisms, forming soil ag-gregates and humus-coated soil minerals.

Through their feeding and burrowing activi-ties, earthworms move organic matter throughthe soil enhancing soil aeration, water infiltra-tion, and soil structure. They also improve rootgrowth by creating channels lined with nutrients(79) and help till the soil. They can completely

mix the top six inches of a humid grassland soilin 10 to 20 years (80).

Factors that contribute to an abundant popu-lation of earthworms include inputs of fresh or-ganic matter, a medium-textured soil, thick top-soil, a near-neutral pH, moist but well-aeratedsoil, and moderate temperatures. Tillage, acid-producing fertilizers, insecticides, and poorly-drained soils inhibit earthworm survival (79).

DUNG BEETLES

Dung beetlesimprove nutrientcycling, enhancesoil aeration, andimprove foragegrowth while feed-ing on manure andusing it to providehousing and foodfor their young.Adult dung beetlesare drawn to manure by odor. They use the liq-uid contents for nourishment and the roughageto form a brood ball in which the female lays asingle egg. This brood ball is buried in the soilwhere the larva grows, eating about 40 to 50% of

the interior contents of theball while depositing its ownexcrement. After the larvaemerges, secondary decom-posers readily break downthe remaining dung ball (81).

An adequate populationand mix of dung beetle spe-cies can remove a completedung pile from the soil sur-face within 24 hours (82).This process decreases the po-

tential for ammonia volatilization and nutrientrunoff while making manure nutrients availableto secondary decomposers within the soil pro-file. While moving dung into the soil, dungbeetles create tunnels that en-hance soil aeration and waterinfiltration. Dung removalalso increases forage availabil-ity, since it minimizes the ar-eas that animals are avoidingbecause of the presence of ma-nure.

Through their feeding and bur-rowing activities, earthworms• break down large residues• produce nutrient-rich casts• move organic matter through

the soil• enhance soil aeration, water

infiltration, and soil structure• improve root growth

An adequate popula-tion and mix of dungbeetle species canremove a completedung pile from thesoil surface within 24hours.


Environmental conditions that enhance activi-ties of dung beetles include adequate soil mois-ture levels and warm temperatures. Dung beetlelarvae are susceptible to some insecticides usedfor fly and internal-parasite control for cattle.Both injectable and pour-on formulations ofIvermectin (Ivomec and Doramectin), applied tocattle at the recommended dosages, reduce sur-vival of the larvae for one to three weeks. How-ever, when administered as a bolus, effects ondung beetle populations last up to 20 weeks (83).

carbon-rich forms of organic matter. They alsoform soil aggregates by binding them with fun-gal threads or hyphae.Mycorrhizal fungi en-hance the nutrient andwater uptake of plantsby extending thelength and surface-area of root uptake.

In dry rangelands,crusts composed ofgreen algae, bacteria,cyanobacteria, lichens,and fungi form overthe soil surface. These crusts provide surfacecover, erosion control, and soil aggregation. Theyare also involved in nitrogen fixation and nutri-ent decomposition. Crust organisms are mostactive during the cooler, moister part of the yearwhen plant cover is minimal (2).

AMOEBAS, NEMATODES, AND PROTOZOA

Amoebas, nematodes, and protozoa feed onbacteria and fungi. Nematodes may consumeup to 25% of the bacteria in the soil (84). Accord-ing to one study, nematodes feeding on bacteriaaccelerated litter decomposition by 23% (85). Bothprotozoa and nematodes release nutrients to thesoil system, making them available to plants andother soil organisms.

MUTUALISTIC RELATIONSHIPS

In undisturbed ecosystems, plants and soilorganisms have coevolved to form mutualisticrelationships. Plants provide carbohydrates andother nutrient-rich substances through their rootsystem, providing an excellent source of food forsoil organisms. As a result, populations of soilorganisms involved in nutrient decomposition aregreatest next to plant roots (85). These organ-isms provide plants with nutrients necessary fortheir growth, produce hormones and other chemi-cals that improve plant vigor, and protect the plantagainst diseases. When the plant’s need for nu-trients is low, soil organisms will hold nutrientsin their bodies rather than release them into thesoil solution (10). This mutualistic relationshipis disturbed by cultivation and harvesting. Whenplant roots are removed, populations of soil or-ganisms decrease since they no longer have asource of nourishment and habitat.

Soil organisms are not only responsible forthe mineralization and release of nutrients fromorganic material; they are also important for re-taining nutrients in the soil, improving soil struc-ture through the formation of aggregates andhumus, degrading toxic substances, and sup-pressing diseases. Nutrients held in the bodiesof soil organisms gradually become available forplant uptake and meanwhile they are protectedagainst being lost through leaching, runoff, orother processes. Soil organisms involved in nu-trient cycling release nutrients as they defecateand die. While they are still alive, these organ-isms conserve nutrients within their bodies.

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Soil microorganisms are responsible for• mineralizing nutrients• retaining nutrients in the soil• forming aggregates• degrading toxic substances• suppressing diseases

BACTERIA AND FUNGI

Bacteria and fungi are the most prevalent soilorganisms. Bacterial decomposers feed on rootexudates as well as on plant litter and manure.Maintaining actively growing soil roots providesa nutrient-rich habitat for the growth of manybacterial species. Some species of bacteria areable to detoxify pollutants while other species,particularly rhizobia and cyanobacteria(“bluegreen algae”), are able to fix nitrogen. Bac-terial gels are an important component of soilaggregates. Fungi decompose complex or more


Soil health refers to the ability of soils to func-tion as a productive environment for plantgrowth, an effective filter, and an efficient regu-lator of water flow. Soil mineralogy and chem-istry form the basis for soil composition and soilhealth. However, much of soil health and func-tion depends on an active community of diversesoil organisms. Nutrient cycling, aggregate for-

mation, degradation of toxins, creation of soilpores, and absorption of water and nutrients areall functions of soil organisms.

The activities of soil organisms serve as ef-fective indicators of current land productivityand its ability to withstand degradation. Bymonitoring these indicators, farmers, soil conser-vationists, and other land managers can imple-ment appropriate practices to minimize soil ornutrient losses, enhance nutrient cycling, andincrease plant productivity. The Soil QualityInstitute has taken the lead in developing andpromoting the use of soil health indicators (86).

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Good

Complete cover of for-ages and litter over en-tire pasture.

Diversity of plant spe-cies, including forbs, le-gumes, and grasses,and differences in leafand root growth habits.

Abundant vertical andhorizontal roots.

Many dung beetles andearthworms present.

Wire flag enters soileasily, and does not en-counter hardened areaat depth.

No gullies present; wa-ter running off pastureis clear .

Soil in clumps; holds to-gether when swirled inwater.

Water soaks in duringmoderate rain; little run-off or water ponding onsoil surface.

Medium

Limited bare patches.No extensive bare ar-eas near drainage ar-eas.

Limited number ofspecies and limiteddiversity of growthhabit. Some invasiveplants present.

More horizontal rootsthan vertical.

Few dung beetles andearthworms present.

Wire flag pushed intosoil with difficulty, orencounters hardenedarea at depth.

Small rivulets pre-sent; water runningoff pasture is some-what muddy.

Soil breaks apart af-ter gentle swirling inwater.

Some runoff duringmoderate rainfall,some ponding on soilsurface.

Poor

Extensive bare patchesespecially near wateringor other congregation ar-eas.

Less than three differentspecies, or invasive spe-cies are a major compo-nent of the plant mix.

Few roots; most are hori-zontal.

No dung beetles orearthworms present.

Wire flag cannot bepushed into soil.

Gullies present; waterrunning off pasture isvery muddy.

Soil breaks apart withinone minute in water.

Significant runoff duringmoderate rainfall; muchwater ponding on soilsurface.

Indicator

Pasture cover

Plant diversity

Plant roots

Soil life –macroorganisms

Soil compaction

Erosion

Soil aggregation

Water infiltration

Adapted from the Georgia, Mon-Dak, and Pennsylvania Soil Health Cards (86) Sullivan (88) and USDA (89).

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Bacteria – the most numerous microorganism in the soil. Every gram of soilcontains at least a million of these tiny one-celled organisms. Decompose simpleor nitrogen-rich organic matter. Require moist environments. Also responsiblefor nitrogen fixation, soil aggregate formation, and detoxification of pollutants.

Actinomycetes – thread-like bacteria, which look like fungi. They are decom-posers and are responsible for the sweet, earthy smell of biologically active soil.

Fungi – multicelluar microorganisms that usually have a thread-like structure.Mycorrhizae form extensions on roots, increasing their ability to take up nutri-ents and water. They also transport nitrogen from legumes to grasses. Yeasts,slime molds, and mushrooms are other species of fungi.

Algae – microorganisms that are able to make their own food through photosyn-thesis. They often appear as a greenish film on the soil surface following arainfall.

Protozoa – free-living animals that crawl or swim in the water between soilparticles. Many soil protozoan species are predatory and eat other microorgan-isms. By feeding on bacteria they stimulate growth and multiplication of bacteriaand the formation of gels that produce soil aggregates.

Nematodes – small wormlike organisms that are abundant in most soils. Mostnematodes help decompose organic matter. Some nematodes are predatorson plant-disease-causing fungi. A few species of nematodes form parasitic gallson plant roots or stems, causing plant diseases.

Earthworms – multicellular organisms that decompose and move organic mat-ter through the soil. Earthworms thrive where there is little or no tillage, espe-cially in the spring and fall, which are their most active periods. They prefer anear neutral pH, moist soil conditions, an abundance of plant residues, and lowlight conditions.

Other species of soil organisms – Many other organisms, including dungbeetles, sowbugs, millipedes, centipedes, mites, slugs, snails, springtails, ants,and birds facilitate nutrient cycling. They make residues more available to smallerorganisms by breaking them down physically and chemically and by buryingthem in the soil.

Qualitative “farm-based” and “farmer friendly”indicators are incorporated into soil health cardsspecific to location and farming practice (87).These cards can be used to monitor the relativehealth and productivity of soils, identify areas

of concern, and enhance awareness of the rela-tionships between soil health and crop produc-tion. Below is a soil health card for pastures basedon a compilation of indicators from soil healthcards developed in various locations.

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Provide soil organisms with a balanced diet• Manure and perennial pastures provide food for soil organisms• Succulent materials that are more nitrogen-rich are more rapidly decomposed

than materials that are older and woodier and contain less nitrogen

Provide soil organisms with a favorable environment• Most beneficial soil organisms prefer a well-aerated environment• Decomposer bacteria generally prefer an environment that is moist, has a near

neutral pH, and has easy-to-decompose materials• Decomposer fungi generally prefer an environment that is acid, moderately dry,

and has more carbon-rich, complex organic materials• Continuous plant growth maintains environment of actively growing roots in the

soil. The root or rhizosphere environment is a very nutrien-rich habitat for thegrowth of many soil organisms

Use practices that favor the growth of soil organisms• Maintain a balance between intense grazing and adequate rest or fallow time• Encourage movement of grazing animals across pastures to feed and distribute

manure evenly as well as to kick and trample manure piles• Maintain a diversity of forage species to provide a variety of food sources and

habitats for a diversity of soil organisms

Avoid practices that kill or destroy the habitat of soil organisms• Avoid the use of Ivomectin deworming medications, soil-applied insecticides, and

concentrated fertilizers such as anhydrous ammonia and superphosphate• Minimize tillage and other cultivation practices• Minimize practices that compact the soil, such as extended grazing practices or

grazing wet soils

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Judicious applications of fertilizers and ma-nure enhance plant growth. However, if nutri-ents are applied at the wrong time or in excess ofwhat plants can use, they increase the potentialcontamination of nearby rivers and lakes. Simi-larly, grazing practices can degrade water qual-ity if grazing intensity is too great, if paddocksare used when the soil is too wet, or if the dura-tion of rest periods is too short. Long-term in-tensive grazing practices can negatively affectwater quality, especially when combined withheavy fertilization with either mineral or manurenutrients. Likely impacts include contaminationof groundwater with nitrates and contaminationof surface water with phosphate, sediments, andpathogens (90, 91).

off. High levels of phosphorus in surface watercause eutrophication and algal blooms. Whensources of drinking water have significant algalgrowth, chlorine in the water-treatment processreacts with compounds in the algae to producesubstances that can increase cancer risks.

Unlike phosphorus, nitrogen does not readilybind to soil minerals or organic matter. As a re-sult, it easily leaches through the soil, especiallyif high rainfall follows manure or nitrogen fertil-izer applications and the soil is sandy or grav-elly. High levels of nitrate in ground water usedfor drinking can cause health problems for hu-man babies and immature animals. Managementpractices that minimize the potential for nitrogenleaching include not applying excessive nitrogenand avoiding manure or nitrogen fertilizer appli-cations during times when plants are not activelygrowing.

Erosion occurs when water or wind movessoil particles, resulting in the loss of topsoil andof the nutrients, toxins, and pathogens attachedto these particles. Erosion by water can also trans-port surface-applied manure into lakes, rivers,and streams. Water quality concerns associatedwith erosion include siltation, fish kills, eutrophi-cation, and degraded quality for recreational anddrinking-water uses.

NUTRIENT BALANCES

Water contamination problems associatedwith farming are becoming an increasing societaland political concern. The Federal Clean WaterAct mandates states to minimize non-point-sourcepollution or pollution associated with runoff anderosion, much of this originating from agricul-tural lands (92). Currently, water quality regu-lations are primarily focused on larger farms thathave a high concentration of animals and use highinputs of purchased feeds. Societal concernsabout farming operations are increasing as morenon-farm families move into rural areas and ur-ban growth decreases the distance between farmand non-farm community members.

On farms that have high numbers of animals,a limited land area, and high use of feeds thatare not grown on the farm, nutrient imbalancesexist. This is because the amount of nutrients

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NUTRIENT LOSS PATHWAYS

If more manure or fertilizer nutrients are ap-plied to pastures than are used in the growth offorage crops, excess nutrients will either accu-mulate in the soil or be lost through leaching,runoff, or erosion. Nutrient accumulation occurswhen minerals in the soil have the ability to bindor hold particular nutrients. Sandy or silty soilsor soils with a near-neutral pH do not bind phos-phorus well. When more phosphorus is appliedto these soils than is used for plant growth, theexcess phosphorus can easily be dissolved andcarried away by runoff water to lakes andstreams. Both acid clay soils and soils with ahigh calcium carbonate content have a strong abil-ity to bind large amounts of phosphorus. If onlymoderate excesses of phosphorus are applied tothese soils or if excess phosphorus is applied tothe soil only occasionally, these soils will be ableto bind the excess phosphorus and hold it againstleaching. However, if phosphorus fertilizers ormanure are continually applied at high rates,phosphorus levels will eventually build up in thesoil to the extent that soils will no longer be ableto hold onto the additional phosphorus and theseexcesses will be susceptible to loss through run-

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that accumulate in the animal manure isgreater than the needs of all crops being grownon the farm. Maintaining a balance between theamount of nutrients added to the soil as manureand fertilizer and the amount of nutrients removedas forages, hay, crops, or livestock is critical forproductive crop growth and water quality pro-tection. If more nutrients are removed than arereturned to the system, crop production will de-cline. If more nutrients are added than can beused for productive crop growth, nutrients willbuild up in the soil, creating a high risk for leach-ing, runoff, and water contamination.

While environmental regulations primarilytarget large farms, these are not the only live-stock operations at risk for contaminating waterquality. Often, smaller livestock farms pose morerisk than larger operations. For instance, onsmaller dairy farms the barn is commonly locatednear a stream because it was built prior to ruralelectrification and the ability to pump water fromwells or streams to watering troughs. On manysmall livestock operations, animals have accessto paddocks located near a well head or overhighly permeable soils because land area is lim-ited. Riparian areas are less likely to be protectedby fencing or buffer areas. On farms withoutadequate manure storage facilities, manure is of-ten applied to poorly drained or frozen fieldsduring the winter, resulting in a high potentialfor surface water contamination. In addition, onsmaller farms, necessary equipment or labor isoften not available to properly apply manure ac-cording to a nutrient management plan. Carefulmanagement of grazing and manure-handlingpractices is critical on all farms in order to pro-tect water resources.

PATHOGENS IN MANURE

Although not directly related to nutrient cy-cling, pathogens are a critical water quality con-

Manure or fertilizers should be appliedwhen the nutrients in these materials canbe most effectively used for plant growthand production, and never to ground thatis snow-covered, frozen, or saturated.

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cern associated with manure management. Ani-mal grazing and manure applications can con-taminate water bodies not only with excess nu-trients but also with parasites in feces. Parasitesof greatest concern are E. coli, Giardia, andCryptosporidium. E. coli is of most concern to ru-ral residents dependent on well water and of lim-ited concern to public water users since this para-site is killed by municipal water purification andtreatment processes. Typically, this parasitecauses mild to moderate gastrointestinal prob-lems. However, new strains of E. coli have killedpeople who are very young, very old, or haveweakened immune systems. Giardia andCryptospordium are pathogens with a dormantstage that is very resistant to purification treat-ment. Almost all municipal water treatment fa-cilities are required to use secondary filtrationprocesses that remove these resistant forms fromthe water supply. Most private wells, however,do not have the capability of filtering out thesepathogens. Like the virulent strain of E. coli, Gia-rdia and Cryptospordium cause gastrointestinalproblems that can be fatal for people with weakor undeveloped immune systems.

Minimizing the risk of pathogen movementinto water bodies involves ensuring that animals,especially young calves, are not exposed to, orkept in conditions that make them susceptibleto, these diseases. Any manure that potentiallycontains pathogens should either be completelycomposted before application, or applied to landfar from streams and at low risk of erosion orrunoff (93).

PASTURE MANAGEMENT PRACTICES TO

REDUCE RISKS OF PATHOGEN

CONTAMINATION

Manure or fertilizers should be applied whenthe nutrients in these materials can be most ef-fectively used for plant growth and production,and never to ground that is snow-covered, fro-zen, or saturated. Under such wet or frozen con-ditions, manure or fertilizer nutrients are notbound by soil particles. Instead, these nutrientsare lying unbound on the soil surface where theyhave a high potential to be carried away by run-off into lakes or streams. Pathogens in manureapplied to frozen or snow-covered soil will notbe in contact with other soil organisms. In addi-tion, most predatory soil organisms will be in a


dormant state and unable to decrease pathogennumbers before snowmelts or heavy rainfallscause runoff.

Areas that need to be protected from con-tamination by nutrients and parasites in animalfeces include well heads, depressions at the baseof hills, drainage ways, rivers, streams, and lakes.Well heads and water bodies need protectionbecause they serve as drinking and recreationalwater sources, while foot slopes and drainageways have a high potential for nutrient runoffand transport of contaminants to water bodies.

local health departments can test wells to deter-mine nitrate concentrations.

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Nitrate is not held by soil particles and is eas-ily leached, especially through porous soils, suchas sandy soils or soils with cracks or fissures thatallow for rapid movement of excess nitrogenthrough the soil profile. Where excess nitrogenis not applied, nitrate leaching in pastures is mini-mal. High nitrate leaching losses were observed,however, when orchard-grass pastures in Penn-sylvania were fertilized with 200 pounds per acreof nitrogen as ammo-nium nitrate (45). Theseresearchers also calcu-lated that a stocking ratefor Holstein dairy cowsof 200 animal dayswould result in nitrateleaching from urine inexcess of drinking-water standards (10 mg/liter)(45). In pastures where nitrogen was providedby nitrogen-fixing legumes, nitrate leaching wasminimal when environmental conditions werenormal. But high nitrate leaching was observedwhen a severe drought followed good growingconditions, causing legume nodules to die andrelease nitrogen into the soil (20).

Nitrate concentrations greater than 10 ppmin well water may cause nitrate toxicity or meth-emoglobinemia. This ailment, which affects in-fant children as well as young chickens and pigs,and both infant and adult sheep, cattle, andhorses, increases nitrate concentration in thebloodstream and prevents the uptake and use ofoxygen, thus causing suffocation. Pregnant ani-mals that are affected may recover, then abortwithin a few days (21). Personnel associated with

High nitrate leaching occurs when a severedrought follows good growing conditions,causing legume nodules to die and releasenitrogen into the soil.

Phosphorus can be transported from fieldsor pastures into lakes or streams either as a com-ponent of erosion or within runoff water. Phos-phorus that is dissolved in runoff water has agreater effect on water quality than phosphorusthat is attached to soil particles transported towater bodies by erosion (94). This is because thedissolved phosphorus is more available for useby algae and other aquatic organisms that causeeutrophication, noxious greening of water bod-ies, and fish kills. Phosphorus associated withsoil particles tends to settle to the lake or riverbottom where it remains biologically stable oronly slowly available for use by aquatic organ-isms.

DISSOLVED PHOSPHORUS

In pastures, sources of dissolved phospho-rus include manure or phosphorus fertilizers ly-

ing on the soil surface,and wet soils that have ahigh phosphorus concen-tration. Runoff watercan readily dissolvesoluble phosphorus inmanure or phosphorusfertilizers. When the

amount of phosphorus in soil exceeds the abilityof soil particles to bind onto it, the excess phos-phorus can readily be dissolved and transportedby runoff water, especially when soils are satu-rated. Dissolved phosphorus has the greatestpotential for being transported from pastures intowater bodies when rainfall is heavy, when highlevels of phosphorus are present either on thesurface of the soil or within the soil, and whenpastures are located within 350 feet of water bod-ies (95).

Increasing forage diversity generally de-creases runoff potential. Care should be takento combine species, such as bunch-grasses, thatenhance water infiltration but expose the soil sur-face between clumps (96), with closer-growingspecies such as tall fescue or prostrate speciessuch as white clover. A combination of native


forages and low-growing, shade-tolerant plantscould enhance both water infiltration and cattleproduction (D. Brauer, personal communication).Setting up paddocks on the contour can also al-low downslope paddocks that are regeneratingafter grazing to serve as buffer strips for upslopepaddocks that are currently being grazed. Po-tential runoff from manure can also be reducedby applying it to alternate paddocks set up ascontour strips (D.E. Carman, personal commu-nication).

PHOSPHORUS ASSOCIATED WITH EROSION

Soil-attached phosphorus can be transportedto water bodies by erosion. Low-level sheet ero-sion contributes more phosphorus than higher-impact rill or gully erosion. This is because sheeterosion primarily transports nutrient-enrichedtopsoil, manure, and plant residues while gullyerosion transports more nutrient-poor subsoil(27). As with runoff, the amount of phosphorustransported by erosion is greatest during intenserainfalls or snowmelts. Pasture soils that arecompletely covered by vegetation are protectedagainst the forces of erosion. Erosion occurs pri-marily when soils are bare and land is sloping.

IMPACT OF PHOSPHORUS

CONTAMINATION ON WATER QUALITY

The impact of phosphorus runoff on streamor lake water quality is greatest during summerand fall. While spring rains or snowmelts maytransport a greater total amount of phosphorus,the large amount of water in the runoff dilutesthe phosphorus so that it is in a relatively lowconcentration when it reaches water bodies. Incontrast, intense rains falling on soils and pas-tures during the summer are likely to run offrather than soaking into dry, hard soils. Whenintense rains fall on pastures with surface-ap-plied manure or phosphorus fertilizers, runoffwater will carry a high concentration of dissolvedphosphorus into streams. If these streams haverelatively low water flows, the runoff water willcreate a high concentration of phosphorus in

streams, which then causes algae and other nui-sance plants to grow (27).When the amount of phosphorus in soil ex-

ceeds the ability of soil particles to bindonto it, the excess phosphorus can readilybe dissolved and transported by runoffwater, especially when soils are saturated.

The type of phosphorus fertilizer used influ-ences the potential risk of water contamination.Highly soluble fertilizers such as superphosphatepresent a greater short-term potential for phos-phorus loss since they are easily dissolved andtransported. In the long term, however, less-soluble fertilizers, such as dicalcium phosphate,may pose a greater risk. This is because less-soluble fertilizer remains on the soil surface andavailable for dissolution and runoff for a longertime (27). Impacts on water quality from sedi-ment-attached phosphorus fertilizer have beenobserved to persist for up to six months (97).Runoff risks can be substantially decreased if fer-tilizers are incorporated into soil and applied ac-cording to a nutrient management plan.

PHOSPHORUS INDEX

The phosphorus index was developed to ad-dress federal and state water quality guidelineswhile recognizing that phosphorus movement isinfluenced by local environmental conditionsand land management practices. Each state isdeveloping their own phosphorus index to en-sure that it is appropriate to local conditions.Each phosphorus index contains a componentrelated to phosphorus sources, soil-test phospho-rus, manure phosphorus, and fertilizer phospho-rus. (Soil-test phosphorus accounts for the plant-

• Excessive phosphorus stimulatesgrowth of algae and aquatic weedsin lakes and streams

• Rapid algal and aquatic-weed growthdepletes oxygen from water, leadingto death of fish

• Outbreaks of certain aquatic organ-isms dependent on high phosphoruslevels can cause health problems inhumans, livestock, and other animals

• When water that has high algalgrowth is chlorinated for use as drink-ing water, carcinogenic substancesare formed

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available or soluble phosphorus in the soil, de-rived either from the mineral base of the soil orfrom decomposing organic matter.) The poten-tial for manure or fertilizer phosphorus to be lostthrough runoff depends on the amount applied,how it was applied, and when it was applied.Manure and fertilizer incorporated into the soilat rates required for crop growth, and at or justprior to the time of crop production, pose mini-mal risk to water quality. Conversely, surface-applying excessive amounts of manure or fertil-izer when crops are not actively growing or whenthe soil is saturated, frozen, or snow-covered willpose high risks for phosphorus runoff. However,a high concentration of phosphorus in the soil orapplied to the soil will not pose a risk to waterquality unless there is a means of transportingthis phosphorus to water bodies. Methods fortransporting phosphorus from farm fields towater bodies include erosion, runoff, and flood-ing. Locations that have a high source of phos-phorus and a high risk of transport are criticalsource areas or locations where land managersneed to carefully consider risks of phosphoruslosses.

CONTAMINANT TRANSPORT

THROUGH DRAINS

Unfortunately, the advantage that subsurfacedrainage provides in decreasing runoff potentialmay be overshadowed by the ability of drainagesystems to directly transport nutrients from fieldsto waterways. Most subsurface drainage sys-tems were installedprimarily for produc-tion reasons: to allowfarmers to work theirfields earlier in theyear and to minimizeplant stunting anddisease problems as-sociated with satu-rated soils. Sincemany of these sys-tems were installedbefore agriculturalimpacts on waterquality became a societal concern, agriculturaldrains often empty directly into streams and riv-ers.

Because artificial drainage makes fields drier,farmers can drive tractors or other equipmentonto these fields earlier in the year. Farmers whohave a full manure-storage system to empty, orwho have time constraints for spreading manurein advance of planting, may be tempted to applymanure and fertilizers to these fields during timeswhen the soil would be wet if it were not drained.Farmers with a limited land base may want tograze these fields when the weather is wet. How-ever, to protect water quality, these fields shouldbe managed as though artificial drainage had notbeen installed. Nutrients in fertilizers or manurecan leach through the soil to drainage pipes. Ifartificially drained fields are used for nutrient ap-plications or grazing while water is flowing outof drainage outlets, drainage water can carrythese leached nutrients directly to streams or riv-ers.

In soils with subsurface drainage, cracks andchannels provide a direct pathway for nitrate,phosphorus, or soluble manure to move from thesoil surface to subsurface drains (6, 78). Becausethese channels are relatively large, contaminantsare not absorbed by soil particles or biologicallytreated by soil organisms (27). Soil cracks or

Artificial subsurface drainage makes normallywet soils drier, and decreases the wet period forseasonally wet soils, by allowing more water toseep into the soil profile. Subsurface drainagehas been shown to decrease water runoff by 72%and total phosphorus losses due to runoff by 50%(5).

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During wet periodsof the year, artifi-cially drained fieldsshould be managedas though they werenot drained. Grazing,manure spreading,and fertilizer applica-tions should beavoided while drainsare flowing.

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Critical Source Area for P

PhosphorusTransport

• Soil erosion• Water runoff• Flooding frequency

PhosphorusSource

• Soil test P• Manure and fertilizer P• Application method and

timing• Grazing manage-

ment

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channels develop through earthworm burrowing,death and decomposition of taproots, and soildrying. The direct connection of cracks or chan-nels in soils to artificial drainage pipes can trans-port phosphorus and pathogens from manure ap-plications directly to drainage outlets within anhour after the onset of a heavy rain (6). One re-search study showed that a single rotational graz-ing event doubled the amount of sediment andincreased the amount of dissolved phosphorusin tile drainage water 15-fold compared to anungrazed site (5).

MANAGEMENT PRACTICES

To minimize the potential for water contami-nation, land that is artificially drained should notbe grazed or have fertilizer or manure appliedduring times when drainage water is flowing fromthe field or just prior to a rainstorm. Alterna-tively, contaminated water flowing out of tiledrains should not be allowed to empty directlyinto rivers or streams. Instead, it should be di-rected to a grassed filter or buffer area, or treatedin a wetlands area where biological and chemicalprocesses lower contaminant levels through sedi-mentation and absorption (27).

ers to capture sediments and absorb runoff wa-ter.

Riparian buffers are limited in their ability toremove soluble phosphorus and nitrate from run-off water, especially if flows are intense (98).During heavy rainstorms or rapid snowmelts,buffers generally have limited effectiveness forcontrolling the movement of runoff-borne nutri-ents into water bodies. This is because waterfrom these heavy flows concentrates into rapidlymoving channels that can flow over or throughbuffer areas.

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A well-designed buffer with a combinationof trees, shrubs, and herbaceous plants has theability to trap sediments and nutrients associatedwith the sediments. Buffers also provide habitatfor river-bank and aquatic animals. An effectivebuffer for trapping sediments contains a combi-nation of grasses and herbaceous plants that areable to catch sediments in their foliage or resi-dues. The root channels around actively grow-ing plants will also absorb slow-moving runoffwater and plants in the buffer area will use trans-ported nutrients for their growth. Regular har-vest and removal of buffer vegetation can delayor prevent the buildup of nutrients in the bufferarea. However, harvests must be conducted in amanner that does not decrease the ability of buff-

As phosphorus is continually transportedinto buffers, soils in the buffer area willeventually lose their ability to hold addi-tional phosphorus, thus limiting their ef-fectiveness to control phosphorus move-ment into streams.

The continual transport of phosphorus-richsediments into buffers will cause a buildup ofhigh concentrations of phosphorus in buffer ar-eas. Eventually, these areas will lose their abilityto hold additional phosphorus. Buffer areas canactually become a source of phosphorus enteringwater bodies, rather than an area that capturesphosphorus before it enters water bodies (99).

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Tile drainage water should be directed to agrassed filter or buffer area, or treated in awetlands area where biological andchemical processes lower contaminantlevels.

When grazing animals have continuous, un-limited access to riparian areas, their activitiesbreak down stream banks, alter stream flow,cause decreased vigor of stream-bank vegetation,and diminish the species diversity and popula-tions of fish and aquatic wildlife (100, 101). Cattle


growth, bank protection, and sediment entrap-ment (104).

Pasture management practices should dis-courage animals from congregating in the streamor on the stream bank, where their manure canpollute water. Shade, salt licks, and other sourcesof supplemental nutrients should be located atleast 15 feet from the stream bank to provide abuffer between areas of manure deposition andthe stream (100).

The season in which riparian areas are grazedis also an important consideration if water qual-ity is to be protected. Grazing in the spring orearly summer followed by complete livestockremoval in the summer allows riparian plant re-growth to occur before the dormant period inthe fall. Animals will damage stream banks ifthey are allowed to graze riparian areas in thewinter when soils are freezing and thawing or inthe spring when soils are wet. During droughtconditions, streambanks should not be grazedsince vegetation will be slow to recover. Ani-mals should not be allowed to graze riparian ar-eas in the summer, when hot dry conditions wouldencourage cattle to congregate in the water (103).Stream banks that have a high soil moisture con-tent or a fine soil texture, or that are prone toerosion, are subject to early-season grazing dam-age and should not be grazed in the spring or notuntil they have dried (104). Use of floating fencesand graveled access areas can control animal ac-cess to water, minimizing the impacts on stream-bank stability and ecology.

grazing in riparian areas trample on streamsideand aquatic organisms, disturb the habitat of theseorganisms, decrease oxygen availability by sus-pending bottom sediments, and contaminatestreams by directly depositing manure and urine(102). Animal movement along streambanks orwithin streams also contributes to bank erosion.In addition, grazing activities alter the amountand type of plant residues available for the growthand reproduction of riparian organisms (90).

Limiting animal access to riparian areasallows a thick vegetative turf to developthroughout the paddock, which stabilizesstream banks and reduces stream-bankerosion.

Managed grazing of riparian areas can pro-tect water quality and improve riparian habitat.In Wisconsin, researchers studying intensive ro-tational grazing practices restricted livestock ac-cess to riparian areas to 5 to 20 days per season.Limiting animal access to riparian areas alloweda thick vegetative turf to develop throughout thepaddock, which stabilized stream banks and re-duced streambank erosion (102). For dairy cattle,each grazing period should last only 12 to 24hours, while beef cattle and sheep can be grazedfor 3 to 4 days each time (103). Grazing shouldnot be allowed to reduce herbage stubble to lessthan 4 to 6 inches in height. This will protectwater quality by providing adequate plant


Minimize congregation of animals in pastures• Use practices that encourage the movement of animals across paddocks• Avoid overgrazing of pastures

Minimize the potential for nitrate leaching• Encourage animal movement across paddocks• Maintain a healthy cover of actively growing forages across paddocks• Rotate pastures to maximize nutrient uptake by plants

Minimize the potential for nutrient runoff• Do not apply fertilizers or manure to saturated, snow-covered, or frozen ground• If possible, compost manure before applying it to soil. This will minimize pathogen

populations while transforming nutrients into more stable compounds• Do not use pastures that are wet, flooded, or saturated• Use practices that favor populations of soil organisms that rapidly incorporate ma-

nure into the soil• During cold or wet weather, do not use pastures that are located next to a river,

stream, or waterway• Recognize that buffers are not effective in controlling the movement of nutrients car-

ried by runoff water, especially when flows are intense

Minimize the potential for erosion• Maintain a complete cover of forages and residues across the surface of all pad-

docks• Use practices that minimize the congregation of animals or the repeated trampling of

animals on the same lounging area or pathway• Riparian areas should only be grazed using short-term intensive grazing practices,

and then only during spring and early summer• Maintain riparian buffers (including a combination of herbaceous plants, trees, and

shrubs) adjacent to rivers, streams, and lakes to act as a filter for eroded soil andother contaminants

Minimize water contamination from artificial drainage systems• During wet weather, do not use pastures that are on artificially-drained land• Modify outlets from drainage ways to treat drainage water in wetlands or on filter

areas before it flows into streams or other water bodies

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97. Cooke, J.G. 1988. Sources and sinks ofnutrients in a New Zealand hill pasturecatchment: II. Phosphorus. HydrologyProceedings. Vol. 2. p. 123-133.

98. Tate, K.W., G.A. Nader, D.J. Lewis, E.R.Atwil, and J.M. Connor. 2000. Evaluation ofbuffers to improve the quality of runoff fromirrigated pastures. Journal of Soil and WaterConservation. Vol. 55, No. 4. p. 473-478.

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101. Clark, E.A. and R.P. Poincelot. 1996. TheContribution of Managed Grasslands toSustainable Agriculture in the Great LakesBasin. The Haworth Press Inc., New York.

102. Lyons, J., B.M. Weigel, L.K. Paine, and D.J.Undersander. 2000. Influence of intensiverotational grazing on bank erosion, fishhabitat quality, and fish communities insouthwestern Wisconsin trout streams.Journal of Soil and Water Conservation. Vol.55, No. 3. p. 271-276.

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American Forage and Grassland Council.Gerorgetown, TX.

Mission statement: “To promote the use offorages as economically and environmentallysound agriculture through education, commu-nication, and professional development ofproducers, scientists, educators and commercialrepresentatives and through communicationwith policy makers and consumers in NorthAmerica” <http://www.afgc.org>.

Grazing Lands Conservation Initiative

A national effort to provide high-quality techni-cal assistance on privately owned grazing landsand increase the awareness of the importance ofgrazing land resources. <http://www.glci.org/>.

Grazing Lands Technology Institute (GLTI)Provides technical excellence to the NaturalResources Conservation Service (NRCS) andother appropriate customers in the acquisition,development, coordination, and transfer oftechnology that meets the needs of grazing landresources, landowners and managers, and thepublic. <http://www.ncg.nrcs.usda.gov/glti/homepage.html>, or contact your county orregional NRCS office.

Cooperative Extension Service.

Educational and technical assistance that linksfarmers and ranchers with university researchexpertise. Many county or regional officesaddress grazing practices. To identify yourlocal office see <http://www.reeusda.gov/1700/statepartners/usa.htm>.

Natural Resource, Agriculture, and Engineer-ing Service. Ithaca, NY.

Coordinates and publishes proceedings fromconferences on agricultural and environmentalissues. Also publishes technical and practicaldocuments on manure management,composting, and animal housing. <http://www.nraes.org>.

General Grazing

Clark, E.A. and R.P. Poincelot. 1996. The Contri-bution of Managed Grasslands to SustainableAgriculture in the Great Lakes Basin. TheHaworth Press Inc., New York.

An easy-to-read but technically-based discus-sion of the relations between grazing manage-ment, forage production, and soil quality.

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Emmick, D.L. and D.G. Fox. 1993. PrescribedGrazing Management to Improve PastureProductivity in New York. United StatesDepartment of Agriculture Soil ConservationService and Cornell University. <http://wwwscas.cit.cornell.edu/forage/pasture/index.html>.

Gerrish, J. and C. Roberts (eds.) 1996 MissouriGrazing Manual. University of Missouri.Columbia, MO.

Short papers addressing forage production andnutrient management in pastures.

Pearson, C.J. and R.L. Ison. 1987. Agronomy ofGrassland Systems. Cambridge UniversityPress. Cambridge.

Technical discussion of forage biology andproduction, nutrient availability, and animalnutrition on forages.

Stockman Grass Farmer Magazine

The nation’s leading publication on grass-basedlivestock systems. Order information <http://stockmangrassfarmer.com/>.

Terrill, T. and K. Cassida. 2001. AmericanForage and Grassland Council Proceedings.American Forage and Grassland Council.Gerorgetown, TX.

http://www.afgc.org

http://www.glci.org/

http://www.ncg.nrcs.usda.gov/glti/homepage.html


http://www.reeusda.gov/1700/statepartners/usa.htm

http://www.reeusda.gov/1700/statepartners/usa.htm

http://www.nraes.org


http://wwwscas.cit.cornell.edu/forage/pasture/index.html



http://stockmangrassfarmer.com/



Unsander, D., B. Albert, P. Porter, A. Crossley,and N. Martin. No date. Pastures for Profit. AGuide to Rotational Grazing. University ofWisconsin Extension. Madison, WI. Availableat <http://www.uwrf.edu/grazing/>.

Soil Quality and Soil Conservation

Magdoff, F. and H. van Es. 2000. BuildingSoils for Better Crops, Second Edition. Sus-tainable Agriculture Network. HandbookSeries Book 4. Beltsville, MD.

Easy-to-read descriptions of concepts regardingsoil quality and agricultural managementpractices to enhance soil quality. Althoughmany of the practical management descriptionsare oriented more towards field crops than tograzing systems, the concepts of soil qualityprotection and management are the same.

Edwards, C. 1999. Soil Biology Primer.United States Department of Agriculture,Natural Resources Conservation Service.Washington, D.C. Order information <http://www.statlab.iastate.edu/survey/SQI/soil_biology.htm>

A well-illustrated overview of soil organismsand their impact on soil quality.

Cavigelli, M.A., S.R. Deming, L.K. Probyn, andR.R. Harwood (eds). 1998. Michigan FieldCrop Ecology: Managing biological processesfor productivity and environmental quality.MSU Extension Bulletin E-2646. Michigan StateUniversity Extension Service, East Lansing, MI.

A well-illustrated overview of nutrient cycles inagricultural systems, the organisms that affectthese systems, and the impact of environmentalconditions and management practices on theactivities of these organisms.

Journal of Soil and Water Conservation.Technical articles on soil conservation researchand practices. Many articles pertain to grazingsystems. Order information: <http://www.swcs.org/f_pubs_journal.htm>

Whitehead, D.C. 2000. Nutrient Elements inGrassland Soil-Plant-Animal Relationships.CAB International Publishing. Wallingford,Oxon, UK.

An excellent technical resource on nutrient cyclecomponents and interactions in grazing systems.

Undersander, D. and B. Pillsbury. 1999. Graz-ing Streamside Pastures. University of Wis-consin Extension. Madison, WI.

An easy-to-read overview of the potential risksand benefits associated with riparian grazingpractices.

Water Quality Protection

Sharpley, A.N., T. Daniel, T. Sims, J.Lemunyon, R. Stevens, and R. Parry. 1999.Agricultural Phosphorus and Eutrophication.ARS-149. United State Department of Agricul-ture / Agricultural Research Service. Washing-ton, D.C. Order information: <http://www.soil.ncsu.edu/sera17/publicat.htm>.

An illustrated, easy-to-read discussion describ-ing the impact of environmental conditions andland management practices on the risk forphosphorus runoff from agricultural lands.

Daniels, M., T. Daniel, D. Carman, R. Morgan,J. Langston, and K. VanDevender. 1998. SoilPhosphorus Levels: Concerns and Recommen-dations. University of Arkansas. Division ofAgriculture. Cooperative Extension Service.Accessed at: <http://www.soil.ncsu.edu/sera17/publicat.htm>.

NRAES. 2000. Managing Nutrients andPathogens from Animal Agriculture. NaturalResource, Agriculture, and Engineering Ser-vice. Ithaca, NY.

Proceedings from a conference that includedresearch reports, field experience, and policydiscussions. Available from <http://www.nraes.org>.

http://www.uwrf.edu/grazing/

http://www.statlab.iastate.edu/survey/SQI/soil_biology.htm



http://www.swcs.org/f_pubs_journal.htm

http://www.swcs.org/f_pubs_journal.htm

http://www.soil.ncsu.edu/sera17/publicat.htm







��

Rotational Grazing – University Programs

Center for Grassland Studies - University ofNebraska-Lincoln <http://www.grassland.unl.edu/index.htm>.

Purdue Pasture Management Page- PurdueUniversity Cooperative Extension <http://www.agry.purdue.edu/ext/forages/rota-tional/>.

Texas Agricultural Extension Service. ExtensionResource Center <http://texaserc.tamu.edu/catalog/query.cgi?id=433>.

Controlled Grazing of Virginia’s Pastures –Virginia Cooperative Extension <http://www.ext.vt.edu/pubs/livestock/418-012/418-012.html>.

Grazing Dairy Systems at the Center for Inte-grated Agricultural Systems – University ofWisconsin – Madison <http://www.wisc.edu/cias/research/livestoc.html#grazing>.

Pasture Management & Grazing – University ofWisconsin Extension <http://www.uwrf.edu/grazing/>.

Grasslands Watershed Management – ClemsonUniversity <http://grasslands.clemson.edu/>.

Focuses on the role pasture and forage cropproduction can play in helping insure a clean,safe water supply.

Rotational Grazing –Organizations and Agencies

Grazing Lands Conservation Initiative

A national effort to provide high-qualitytechnical assistance on privately owned grazinglands and increase the awareness of the impor-tance of grazing land resourses <http://www.glci.org/>.

Grazing Lands Technology Institute - Grazinginformation from the Natural Resources Con-servation Service. <http://www.ncg.nrcs.usda.gov/glti/homepage.html>.

Stockman Grass Farmer Magazine - Thenation’s leading publication on grass-basedlivestock systems <http://stockmangrassfarmer.com/>.

American Farmland Trust information site ongrass-based farming systems <http://grassfarmer.com/>.

Sustainable Farming Connection’s GrazingMenu- good links to grazing sites <http://www.ibiblio.org/farming-connection/graz-ing/home.htm>.

Why Grassfed Is Best - Jo Robinson explores themany benefits of grassfed meat, eggs, and dairyproducts <http://www.eatwild.com/>.

Archived listings from Graze-L, an internationalforum for the discussion of rotational grazingand seasonal dairying <http://grazel.taranaki.ac.nz/>.

Soil Quality

Soil Quality Institute. United States Departmentof Agriculture. Natural Resources ConservationService. <http://www.statlab.iastate.edu/survey/SQI/>.

Soil quality information sheets, soil qualityindicators, and soil quality assessment methods

Rangeland Soil Quality. Soil Quality Institute.United States Department of AgricultureNatural Resources Conservation Service.<http://www.statlab.iastate.edu/survey/SQI/range.html>.

Information sheets on rangeland soil quality

Soil Biological Communities. United StatesDepartment of Agriculture Bureau of LandManagement. Information sheets. <http://www.blm.gov/nstc/soil/index.html>.

Ingham, E. 1996. The soil foodweb: Its impor-tance in ecosystem health. Accessed at <http://rain.org:80/~sals/ingham.html>.

The Soil Foodweb Incorporated. <http://www.soilfoodweb.com/index.html>.

Soil microbiology, soil ecology information andlaboratory analyses of soil biology.

http://www.grassland.unl.edu/index.htm

http://www.grassland.unl.edu/index.htm

http://www.agry.purdue.edu/ext/forages/rotational/



http://texaserc.tamu.edu/catalog/query.cgi?id=433

http://texaserc.tamu.edu/catalog/query.cgi?id=433

http://www.ext.vt.edu/pubs/livestock/418-012/418-012.html



http://www.wisc.edu/cias/research/livestoc.html#grazing

http://www.wisc.edu/cias/research/livestoc.html#grazing



http://grasslands.clemson.edu/







http://grassfarmer.com/

http://grassfarmer.com/

http://www.ibiblio.org/farming-connection/grazing/home.htm



http://www.eatwild.com/

http://grazel.taranaki.ac.nz/

http://grazel.taranaki.ac.nz/

http://www.statlab.iastate.edu/survey/SQI/

http://www.statlab.iastate.edu/survey/SQI/

http://www.statlab.iastate.edu/survey/SQI/range.html

http://www.statlab.iastate.edu/survey/SQI/range.html

http://www.blm.gov/nstc/soil/index.html

http://www.blm.gov/nstc/soil/index.html

http://rain.org:80/~sals/ingham.html

http://rain.org:80/~sals/ingham.html

http://www.soilfoodweb.com/index.html

http://www.soilfoodweb.com/index.html


IP136

By Barbara BellowsNCAT Agriculture Specialist

Edited by Richard EarlesFormatted by Gail M. Hardy

December 2001

The electronic version of Nutrient Cycling inPastures is located at:HTMLhttp://www.attra.ncat.org/attra-pub/nutrientcycling.htmlPDFhttp://www.attra.ncat.org/attra-pub/PDF/nutrientcycling.pdf

SoilFacts. Soil science related publications fromNorth Carolina State University. Includes:Poultry Manure as a Fertilizer Source, GoodSoil Management Helps Protect Groundwater,Nitrogen Management and Water Quality, andSoils and Water Quality <http://ces.soil.ncsu.edu/soilscience/publications/Soilfacts/AG-439-05/>.

United States Department of Agriculture –Agricultural Research Service. <http://www.nps.ars.usda.gov/>.

Research programs addressing soil and waterquality, rangeland, pastures, and forests, andintegrated agricultural systems.

Water Quality

Pellant, M., P. Shaver, D.A. Pyke, and J.E.Herrick. 2000. Interpreting Indicators ofRangeland Health. Version 3. Technical Refer-ence 1734-6. National Sciene and TechnologyCenter Information and CommunicationsGroup. Denver, CO. <http://www.ftw.nrcs.usda.gov/glti/pubs.html>.

SERA-17. Minimizing Phosphorus Losses fromAgriculture. <http://www.soil.ncsu.edu/sera17/publicat.htm>.

National, multi-agency information on phospho-rus fate and transport, including the develop-ment of the phosphorus index.

United States Environmental Protection AgencyDepartment of Water. 1999. Laws and Regula-tions, Policy and Guidance Documents, andLegislation. Accessed at: <http://www.epa.gov/OW/laws.html>.

Concentrated Animal Feeding Operations(CAFOs) Effluent Guidelines for larger scalefarms. <http://www.epa.gov/ost/guide/cafo/index.html>.

Focuses on confinement systems but many of thenutrient management planning guidelines mayalso be appropriate for grazing systems.

Animal Feeding Operations. US EPA Office ofWater. <http://cfpub.epa.gov/npdes/home.cfm?program_id=7>.

EPA’s National Agriculture Compliance Assis-tance Center. <http://es.epa.gov/oeca/ag/>.

Information on environmental laws affectingagricultural operations.

Riparian Grazing

Riparian Grazing Project - University of Califor-nia Cooperative Extension <http://www.calcattlemen.org/riparian_grazing_project.htm>.

Effects of Cattle Grazing in Riparian Areas ofthe Southwestern United States <http://www.earlham.edu/~biol/desert/riparian.htm>.

Managed Grazing and Stream Ecosystems.Laura Paine and John Lyons. < http://www.uwrf.edu/grazing/>.

Driscoll, M. and B. Vondracek. 2001. AnAnnotated Bibliography of Riparian GrazingPublications. The Land Stewardship Project.<http://www.landstewardshipproject.org/resources-main.html>.

mailto:[email protected]?subject=Nutrient Cycling in Pastures

http://ces.soil.ncsu.edu/soilscience/publications/Soilfacts/AG-439-05/



http://www.nps.ars.usda.gov/

http://www.nps.ars.usda.gov/

http://www.ftw.nrcs.usda.gov/glti/pubs.html

http://www.ftw.nrcs.usda.gov/glti/pubs.html



http://www.epa.gov/OW/laws.html

http://www.epa.gov/OW/laws.html

http://es.epa.gov/oeca/ag/

http://www.calcattlemen.org/riparian_grazing_project.htm



http://www.earlham.edu/~biol/desert/riparian.htm





http://www.landstewardshipproject.org/resources-main.html

http://www.landstewardshipproject.org/resources-main.html

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